This unit has been used for the past 50 years and this is one of the best videos I have ever seen - THANKS!!! PS. only video that talks about the "power jumper" AND all of the limit settings. - fact is if you are replacing the unit and have 4 total wires you should "break the jumper" and if you have 3 wires (120v both sides) you need to LEAVE the jumper. The missing wire will be on EITHER side of the jumper! Like he says, running 120VAC into the 24vDC circuit will be very exciting!
wtf?? I have 6 wires! 2 from city power, 2 from the switch transformer transformer and 2 from fan, lol The only way I see it going is 2 wires sharing a single socket, but that is not pictured. If I do what I see, wire 2 lines from city power direct to box on fan side and 2 wires from the transformer direct to box on switch side, then how does the fan work when it's not hooked up?
My furnace is a comfortmaker and It's a 1980 style, it quit turning turning the fan on last year. I didn't know they had these things in them. The fan would stay on and the burner would kick out. Last year though the fan switch wouldn't come on and neither would the fan when it warmed up. You have turn the blower to on before it does. So I reprogrammed the thermostat to the a.c. side to operate the furnace. The furnace still cut off at the certain temperature. I had to adjust the burner. They said it on web it should burn an inch flame. It does better.
Lennox Pluse (10/1987) G1404/5-100-6 still chuging along. Replace flapper about every 4 years. Had to change Fan Limit switch - HOWEVER generic limit switch cause Blower to short cycle. So had to add Delay -Off-Relay set to 4 minutes (that feature was built into original fan limit switch).
Sorry, your message was in the spam. The motor probably went off on overload. Most of these are automatic reset. If it does not reset after approx 1 hour, look for a reset button (probably red) and push it. If the fan will turn easily and still wont start, manually turn the fan with the power on. If the unit starts (keep your hand free), the capacitor has probably failed. If it is stiff, look for oilers over each bearing. Hope this helps. GFM
I have a 40 year old Lennox furnace, and my fan won't automatically shut off when the burners shut down. I tapped on that dial on the fan and limit switch and the fan then would shut off. When I did that, the dial turned slightly and the fan shut off. I replaced the fan motor a couple of years ago. I did have a very dirty air filter but replacing the filter didn't help fix the fan and limit switch. I'll probably replace my furnace next year. Good video.
What is a "fan and limit" failure? Will replacing this switch probably solve my problem? I'm guessing that it does. I just ordered a new one and will replace it soon.
I just replaced my fan limit switch. It was pretty easy to do. The coil in my old limit switch was distorted and rubbing against the tube, which is why it wouldn't rotate back to the "fan off" position when it cooled down. Yes, I did remove the copper strip. Furnace fan is working normally now. Thanks for the great lesson and tips.
Happy Thanksgiving GFM. You have been a such great instructor. I get up every morning before start working I watch your videos then go to a service. Guy Best Air Chicago Inc.
just finished following tip to tap duct work beside switch worked like a charm shut the breaker off first . think i will check furnace come spring .THANK YOU
I have a followup question. I'm looking for a complete explanation of the whole cycle from turning up the thermostat to the burner and blower fan turning on and off. Do you have a video of that? What part exactly turns the burner on and off and the blower on and off?
I did a set of videos on what I call the "antique furnace" that may help. I don't know the age of your furnace, but most of these furnaces used the thermostat to energize the gas valve which started the burners. As the heat exchanger warmed, the heat operated fan switch (the one you have) closed and started the fan. Hope this helps. GFM
If your switch looks like the one in the video, remove it and look at the probe. It comes in 5", 8", and 11 1/2". Get the right length or it may not sense right. 2 ways you can get one are internet parts houses, (I dont recommend any of them, nothing negative just no experience). You may also buy from a local service repair company over the counter. Hope this helps. GFM
If the motor was hot and now is cool, the motor is probably failed. When a fan motor gets stiff bearings, the bearings are damaged and will probably not last long anyway. Looks like a new motor. Good luck GFM
If the limit controls the primary (120v) of the transformer, the jumper must be left in, as it is the voltage source for both the fan motor and the transformer. Hope this helps. GFM
The fan and limit for that unit does have a single pole double throw switch on the fan portion of the fan and limit. So it is special. The general replacement ones that I have seen all have the copper jumper. Happy Thanksgiving GFM
I have one of these on an old Rheem furnace and I can't understand why its wired like it is. The 24V red wire leaves the limit switch and goes strait to Position #1 of the Honeywell s86F intermittent igniter where I am currently missing my 24V signal to turn the GV on. The 24V yellow lead goes from the fan limit strait to the safety switch on the main blower unit, through that and back to terminal Y. That doesn't make any since whatsoever to me but that's the way I found it. As always the coldest day of the year the heat quit working and has not worked since. I have drawn up a schematic of the entire system like I found it.
Thank you Grayfurnace man. I really appreciate that you took the time to document some of your learnings. I have been trying to assist my brother with his Honeywell Limit switch that you appear to be very familiar with. The original part is a L4064T2481 which is not produced anylonger. I have been researching and I believe the replacement should be L4064B2210 . This one seems to be general replacement. The original unit has two low voltage connections in the middle. In reviewing your Honeywell video you mention the replacment and the fact that you would need to remove the copper strip. Can you confirm that the L4064B2210 is the part we need?, and that we will need to remove the copper strip? I appreciate your time and knowledge..
The original part had a helper heater to keep it from short cycling. The part number you have is the proper one if the insertion is 11.5 inches. It may short cycle once before it stays on but there is nothing you can do about that other than separate the on-off temps farther. The copper strip must be removed if the limit switch is in the low voltage circuit. Hope this helps. GFM
Love your videos!! They sure save a working man a lot of money and pain!! Wondering if you can help me. I have a 30 year old Lennox furnace. This morning, the furnace ran as normal and then shut down as normal. A few minutes later, the fan restarted for a few seconds. I went inside and adjusted the 'off' switch to 110 from 100 and it seems to be okay. Initially I had changed it from 100 to 90, and found it cycled again very quickly. So I decided that was the wrong way to adjust it. So, as I said, I moved it to about 110 and it seems okay. Is this a safe thing to do? Is there something else that can be causing this secondary cycling?
I have a honeywell fan (model # 14F0) that stopped spinning. You would hear a buzzing sound (which indicates that its motor is trying to spin but is somehow jammed) but no action. Normally this would be an easy fix, open it & lube it. The problem is I forgot to turn it off when it did that. Since the motor was on but it wasn't spinning, I think something shorted in there. So now when I turn it on there is no buzzing sound or any thing that indicates that electricity is running through it.
Excellent video explaining how this works thank you. I have a Magic Chef furnace that must have gotten an electronic ignition at some point in it's life. The pilot turns on, flame sensor is good, but the main gas valve only opened one time during troubleshooting and I never got the fan at all. Going to check the limit switch out tomorrow, curious if it has failed and cut power to the main gas valve and fan, though I am not sure why the pilot and ignitor stays on in this scenario. Hoping this understanding helps me figure it now now that I know there is more to the circuit than just the flame sensor and valve. The other working furnace shuts down everything when heat shuts off but this must turn the fan on when the still hit burner heats it up again, the gas stays off but the fan comes on again a minute or so after the gas shuts off and then runs for a minute or so until that switch cools down.
If your ignition lights the pilot, then main gas comes on and your situation is the pilot lights but no main gas, clean the flame rod with sandpaper(it is a metal rod about 1/8" diameter in the pilot flame). If that does not help, the ignition control has failed. GFM
@@grayfurnaceman thank you. I cleaned the flame rod first pass but only had cloth. Swapped the whole assembly from a working unit, same thing. Today I cleaned the rod with wire brush and the burner to gas line contact points so they all bonded. I had mixed results with meter yesterday trying to find clean ground. Pilot lights and pulses no main valve fire. I reached in and touched the pilot shroud with a screwdriver and it lit right up. Ran for a while then when back to igniting with just a pilot. Got the idea to clean the shroud, to help the ionization? Maybe the screwdriver close to the flame acted like an antenna for electrons? Cleaning the shroud in place worked great, tested on and off and a cold start 8 times. Gas company came out at my request, supposed to be 7wc and it was 6 and they adjusted as I was leaving. An hr later, same deal no fire. Went back tonight with contact cleaner for the spade connectors and a plan to clean up the corrosion I noticed between the pilot shroud and the main assembly. Thinking about poor ionization/detection/movement of electrons again. I also cleaned the pilot gas line, the end was dirty and I accidentally made it worse, was able to clean with contact cleaner and a single fine bristle of steel brush thru the tiny orifices. Blew thru it, cleaned the heck out of the whole igniter/pilot/flame rod assembly and their contact points to the burner. Fired right up. I removed the igniter to check the pilot without full gas and it still pulses but it's blue now without a yellow tip. Even with gas on high the flame rod doesn't get red hot anymore and it stays lit consistently and lights instantly after the pilot. I know now it's not the heat I need like a thermocouple would function but rather the ionization in the flame. I think the rod was fine but whatever magic happens with the ionization wasn't happening due to poor flame generation by the pilot and bad electrical continuity between components. Maybe the contact cleaner on the spade connectors helped too. I appreciate your videos that helped me catch up on how various components worked. The most important thing was the difference between a flame rod and thermocouple. Once I understood the operation I could make sure the best conditions existed. Hoping it holds up. I think I have finally seen how it's supposed to work and what a good pilot and flame rod activation looks like. The lesson I already knew but was too rushed to bother to do first this time was to clean while I work. No matter what it is you are working on, dirt, corrosion, dust, it all gets in the way of good operation. I wanted it to work first before I bothered cleaning, big mistake.
Also based on your videos I understand my limit switch now. It was all high voltage and if it cuts off it would kill the power to the transformer too. It controls the fan independent of the gas valve operation only responding to the temperature of the heat exchanger. I never got fan because I never reached temperature.
Hi, I have a lenox pulse and the controller is g891tca-8103. It runs fine sometimes for a week or two then shuts off. The green light on the controller goes out as well. Then I shut breaker on and off and it works fine for a week or two. I have cleaned the blower, bottom of the heat exchanger, new filter, and had the board replaced. Flame sensor and spark plug were also cleaned. Have you run across this problem? Now I was thinking if it had anything to do with this limit switch. Any help would be appreciated.
Thanks. Unfortunately it does not reset on its own and there is no reset button. Pushing the fan manually wont work either. I think something shorted out, because the fan was too stiff to spin while the power was left on.
Hello. I have a question that is not related to this video, but I thought to ask since this is a field that you are knowledgeable about. The question will be in the next comment because wouldn't fit here.
So I did one of these today but on a Miller furnace I replaced it the exactly the same wires and everything and for some reason the wires got burned towards the fan and started arcing ugh!
OK took off the limit switch and just pressed at the back of it and the one on the right clicked back in? I hope that makes sense. I put it back on and wired it and it started!!! So it is the limit switch. I'm not sure that fixed it though. I have heat at least. BUT it ran for a minute and the fan never came on? Not sure why I turned the fan on manually and the furnace came back on? I'm going to put it back on auto to see if it works by its self.
This may be a dumb question but is there anyway to know what wires are what coming out of the furnace to connect to this switch? The person who tried to replace the switch on mine did not make note of what wire went where before taking it out and the wire colors don't match 😑
A couple questions. First of all, on a millivolt system, this is also wired to shut off the gas valve, if the fan doesn't come on (e.g., a power outage)? Second, I notice that a few people here have had issues with these units sticking. What is the lifespan of these units, and would it be prudent to replace them on an old furnace BEFORE failure?
What part did you use to replace that switch? I have one like this but can't seem to find a replacement with the same part number. It looks identical. Has a 5 inch probe.
Great tip, i ran into a stuck two stage limit on a icp oil furnace, i bumped it to get it going but just replaces it with a oem part what is the difference besides a 4 day wait from the parts house? And one more thing, how do you know which limits are just 120 and which ones are 120/24, is it on the package? or are they all 120 and you break the copper peice
Hi Grayfurnaceman. You are the man with the answers so I hope it's ok for me to ask also. My neighbor's central furnace lights just fine and the fan comes on for 2 seconds off a split second then on for 3 and so on long and longer for maybe 5 times within 30 seconds then stays on fine and runs fine and cycles off fine. She said it's always done that so probably many years. Mine did that also before I changed my central ac/heat system. Could this be the fan limit switch being faulty?
What is the proper way to recalibrate those switches? Mine was reading about -200 deg F at about 60 deg F. We heated it with a small propane torch to about 500 F and I would hold the dial and pour cold water on the bi-metallic strip. We did that several times and it was close, but still reading colder than ambient temperature. I reached in to the bi-metallic strip with a pair of needle nose pliers and smashed one of the coils a slight bit to make the strip a little longer. I would guess it is within 10 deg F now.
great video...replacing the fan switch. it has the little jumper wire, how do you test to see if 24v or 120? will the two wires on the right read either one when powered up? thanks
I might have an issue with my fan limit switch ( honeywell dial ) My compressor turns on but fan doesn't, unless I rotate the Fan Limit dial slightly, but when the compressor turns off the fan still runs. so in the summertime I just let the fan run, because the thermostat still controls the compressor. I haven't been able to find the video that supports my issue. I have a Janitrol Central Air unit. My house was built in 1986. Appreciate any suggestions. Thanks
Hi, My Lennox G16 conservator III series natural gas furnace fan won't turn on in auto mode however it does turn on in FAN mode. I had an HVAC tech come in and diagnosed it to be bad Fan Limit Control Switch. I myself ordered a brand new Honeywell part from e-bay and replaced it. The problem still persists...any suggestions? Thanks Jas
I have the same limit factory set to 170 degrees as called for for my Heil furnace. The furnace will run for several minutes and this limit will shut down the gas valve and the blower will keep running until the limit cools down and the burners will pick up again. Should I increase the limit temp, .Increase blower speed, or remove and inspect Switch is wired for limit only
Hey Jetstream, I know your post is 6 years old but my Heil gas heater is doing the same exact thing as yours. Did you ever figure your situation out? Was it a crack in your heat exchanger? Please reply if you are still alive (lol)...Thanks
I got this same one,my blower motor stays running ,i isolated the thermostat & still runs,i gotta turn off breaker for it to stop. Could this be the issue ,doesn't have a control board
@@grayfurnaceman thanks for the quick reply, i just replaced panel door switch & still runs,it turns off when i remove bottom panel off,tstat still isolated, i also took wire off that comes from transformer i believe is the common wire that goes to capacitor & it stops,could it be transformer?
@@grayfurnaceman transformer has a plastic piece attach to it were tstat wires connect to it,maybe that could be the issue? Doesnt look like a relay that i can remove
I have a question that hopefully you can help me with related to one of these fan/limit switches. I have a furnace in a house i purchased that short cycles it has a L4064y that does not seem to have the limit switch adjusting tab above the break @ 150* the problem i am having with this is that when the thermal coil trips the fan switch it pops the high limit and cuts the gas valve also causing a short cycle condition. the installation instructions for the 4064y say that it is suppposed to use the 24v hooked to an internal heater to controll fan on. it is not hooked up in this manner on the furnace. my question does is this switch defective or broken missing the adjusting tab for limit or do some just have a fixed limit that is not adjustable so it doesnt have a tab. and would not having the 24v hooked to the heater cause the limit to trip prematurely? Thanks for your time and consideration
hello i have a valley comfort wood/electric combo i have watched your videos on adjusting the 3 point for the kick in and off but this fan keeps staying on for ever. it doesn't stop for 20-30 mins whats the deal thanks Sr
My furnace runs about 90sec before forced air fan starts later when all is off ..the fan comes back on about 2 min later for 30seconds .its a 10yr old big furnace with 1.6gph nozzle does this seem normal...seems to run to long before fan starts.
VN Dustoff If your furnace uses a fan switch like the one in the video, the on and off temps are adjustable. Off can be set at 90 to 100 and on at 130 to 140. Set them farther to eliminate the short cycle after burner shutdown. GFM
Thanks Grayfurnaceman, good video. Hopefully you can solve my problem. I have a 25 year old Rheem Horizontal Furnace. The fan no longer turns off, it continually runs, the thermostat is set to auto and is working correctly, we believe the Fan limit Switch is the problem. The existing switch is a 6 wire switch, Honeywell model L4064T1897, it is no longer manufactured. We can only find 4 wire replacement switches. Can we use a 4 wire replacement switch, if yes, what do we do with the 2 wires not being used any longer, and what is the purpose of those two wires? Thanks!
I have a question for you: my furnace has this type of old honeywell limit switch. The problem is, sometimes after the furnace has run for a long time, the actual switch sticks and won't turn the blower off. I occasionally have to turn the power off and back on to get the blower to stop running. Can these older type limit switches be replaced or fixed? Thanks!
Very common problem. Just to make sure, hit the side of the ductwork near the switch when it sticks on. If it shuts down, the switch is sticking. You can get the switch from internet sources and HVAC dealers. GFM
grayfurnaceman Thanks for the quick response! the problem usually occurs after the furnace has run for a while. I have the thermostat to go from 66 degrees at night to 68 when I get up, and that results in the furnace running for about 15 minutes (the burner). the fan will then stay on for an extra 5 to 10 minutes usually. If the furnace comes on just to maintain a given temp for say, 5 minutes, the fan will then stay on for about a minute. Does that still sound like the fan switch? I don't think there are any blockages in the ductwork and the filter is brand new. Thanks for your help.
***** It depends on the type of furnace. A very old oil fired furnace may run much longer because the heat exchanger is much more massive. Newer ones will shut down in 2 to 5 minutes. You can test this if you place a temp probe in the duct (it must be placed in one of the ducts 2-3 feet from the furnace). Hope this helps. GFM
grayfurnaceman Thanks again! I think I'll just call a service company and get it looked at to be safe. It's been a long time since it's been looked at. I do appreciate the info though.
grayfurnaceman I have one like that and it sticks also. I can barely,barely tap the dial and it shuts off fan. Can this be cleaned or repaired? If not, about how much do they cost? Thanks for any help!
I am confused. What did not come through? Send a pic of what? If you mean my question did not come through, it is there in the full comments. Just to be sure I'll post it again. Thanks.
I would like to add a single pole switch to turn on my furnace air blower, to use as a summer fan to bring cold air from the basement. My fan limit control (white-rodgers) has a manual switch to turn on the fan, but I want to install a switch on the first floor near my thermostat so i don't have to go to the basement to turn it on. I assume the switch can be installed branching off of the fan side terminals of the limit switch. The switch receives 120v both sides and not 24vac. Would this be something that would be safe to do ?
If your furnace is equipped with this switch, there may be a white button on the left side of the switch. When pushed in, it will turn on the fan without the burners. Additionally, you may have a fan center on the furnace that will allow the thermostat to turn on the fan only. GFM
This switch is exactly like mine. My question is about the manual fan "push/pull" did they just leave it off? Is there a plastic pin that needs to be put in it? It appears to just be a hole.
I need to know if that switch has anything to do with the burner cutting off ? It will run for a while then cuts off no gas seems to be getting to it? The Polit will light I can hear the valve clicking, The burner will light sometimes and sometimes not, if not it will cycle out. When it does light a lot of times the flame is pulsating then level out. It will run for sometimes 10 mins then cuts off, trys to light back sometimes it will and sometimes it won't. I do not see any pressure switches or flame indicator, could this be the gas value? or limit control?
UPDATE- I removed the metal shield behind the gas valve between the burners and gas valve and it is working, I put the shield back on and it cuts off? Maybe it's the burner not getting enough o2?
How do I tell if the limit switch is bad? Switch looks just like one in video, on a 16-17 year old propane Amana. Burner starts and as temp gets up the blower starts and runs 30-60 second and blower cuts off. Burner continues and switch turns blower back on for a minute or so... then off. If the house is doing a big warmup the burner keeps going but the blower keeps cycling like this. Replace switch or can an adjustment do it?
grayfurnaceman thanks for your quick reply and your helpful videos. I actually found that video shortly after I posted the question. Yes, the on and off were 20-25° difference. Now I have them approx 100 and 140. I also found the old install manual and it said "set to factory defaults" but didn't bother to say what they are. Guess things can get out of whack--this setting seemed to change on its own--working right and then I started noticing the blower cycling off and on too often.
very good video you can help me I have a problem with my heater tries to turn it on but it sends me the sign of limited swint combustion fallen open I replaced it with a new one but it remains the same if you can help me
I am not sure if I am understanding you right. Are you saying your furnace shuts off the burner because it is too hot and you have replaced the combination fan and limit? It would also help if I knew the fuel used in the furnace and an approximate age. GFM
I am confused what then is rollout switch use for my fan kept running after furnace shut off and never stopped when I went done to check I tapped the limit rollout switch with screw driver and it turned off is this possible
When the limit is open, the fan stays on because the furnace thinks it is too hot. My thought is you have a low airflow problem. Possible dirty filter. If the switch shuts off often, it sometimes will stick open. When you hit it, it broke it loose. Replace the switch and find the low airflow problem. GFM
I have an old rheem furnace from around 1978 or 1979, at one point the furnace was short cycling I think. The fan would come on again for a short time after it had already shut off, someone adjusted it and that stopped. Anyway, now the fan will occasionally keep running after the flame is off, never turning off. Could it be this, or is there a separate fan relay that is sticking. When it happens, if I tap the side of the furnace the fan will shut off.
I have another question. So, the furnace is a Rheem RGMA-080A Furnace. Should I invest money in repairing it? Or should I replace it? I haven't been able to figure out which fan switch goes in it.
Hi Gray, last year at the end of winter my limit switch was replaced along with the thermostat. Now Fall is here, I turn it on and it worked fine. The second time it never worked again.. The fan will come on if I turn it to ON, but the burners never light up. The pilot light is lit and stays on... Any further suggestions in what to do? Thanks, Scott
grayfurnaceman Thanks Gray, I Finally was able to look at this again. I'm not sure how to check the voltage on the gas valve, but I did go ahead and bypass the thermostat and still nothing. I even switched thermostats with the good on, still nothing.. On auto the fan doesn't ever kick in. Of course if you just turn it to on, the fan kicks in, but the burners never light up... Anything else I can check? Thanks!
I hope you got an answer after 7 years but yes. The jumper distributes 120 to both the fan and the limit circuits... look for 3 wires at the control and the limit protection is likely on the primary side of the transformer. If the jumper isn't there or broken off... look for 4 wires and the limit protection is likely on the secondary or 24 volt side of the transfirmer. In either case interrupting power disables the gas valve and shuts off the burners until limit resets after cooling.
Hi Gray, I have a ICP PGAA24C1K1 unit. Unit turns on for 5 minutes and cycles off for 2 minutes. Keeps repeating at those intervals. Me and a tech narrowed it to to either the pressure switch, hi limit switch or the fan control switch. The high limit switch is not easily accessible. I live at 5300 feet above sea level. some say pressure switch might cause issues at this elevation. Any suggestions. Thanks
My guess is the limit is cutting off. It is probably doing its job. I would be looking for air flow problems, such as dirty blower or plugged filter. There could also be a crack in the heat exchanger near the limit. The pressure switch will usually not work at all if it is failed. Hope this helps. GFM
Ok it ain't broke technology so don't fix it but is there is a 21st centurary off the shelf replacement for this mechincal bimetal device? Thx! I knew nothing about oil furnances a few days ago but I am an experienced smart devices maker and engineer. It just seems to me that we can upgrade our decades old furnances without replacing the whole thing. I was pondering using a onewire 18B20 temp probe and a mini brain (e.g. arduino) plus couple relays for the oil burner and blower. Then one could tweek the on-off-over termpature settings and see actual temperatures on (via bluetooth and wifi) a smartphone. I'd throw in some other temperature probes for the burn chamber and maybe the exhaust gas. How about a probes for flue and chamber vaccum, could even have it control the manifold weight. How about a CO detector too. All that can be controller by one little brain. You can even have a simple display and control buttons so as to not require a phone or any wireless connection. But with wifi connection the ower can monitor health of the furnance and be alerted about issues long before they become trouble or dangerous.
I have a Lennox pulse g14. Has no problem heating the house however the fan will turn on and off several times after the heating cycle is satisfied. I adjusted the fan off setting to below 90 degrees and now it only comes on once after the heating cycle. But as soon as the fan shuts off it slowly rotates back to 140 and stays there. The current fan limit switch is a honeywell l4064t2242 it says this part is discontinued do you know which one I can replace it with?
@@grayfurnaceman7640 changed out the fan/limit switch, works great but while I was working on it I found a small propane leak around the top of the gas valve. I dont know If it's the pipes or the gas valve itself. If I shut off the gas to the furnace disconnect the pipes and put thread compound on them and reconnect them with I have to do anything special to light my furnace again? Or should it just resume like normal
@@daltongavers491 First, I would try to isolate the leak by using a soap solution on all fittings. Once it is reassembled, you can just fire it off. It may safety out for the first couple of ignition tries, but it should fire off ok. GFM
I replaced the switch, cut the jumper tab, but now the furnace blower fan will not shutoff. It fixed the problem where the blower fan would not turn on. Any ideas? set to 100 120 200
So once the high limit is reached and power is turned off to the gas valve , at what temperature will the power be restored to the gas valve? You said they dont use these anymore....what do they use now?
Usually, about 180F. Newer furnaces turn on and off the fan with a timer. The fan is also turned on if the temperature of the airflow exceeds a preset temp very similar to the honeywell fan and limit. GFM
I got one more question. I replaced my thermostat and the AC comes on fine and the fan comes on fine. I think my limit control switch might be bad. The thing is I don't know how to test it and mine is not like this one. Mine are two bars laying in parallel beside each other. There is a red black and blue wire. Can I put any limit switch on it or do I have to replace it with the same one? Fanomatic or something like that. And can you tell me how I could test that limit?
grayfurnaceman Thats what the problem was the whole time. There are two on this one. I think one is working know and the other is still not functioning right because its not kicking the fan on. Because the fan wont kick on unless you turn it on manually the furnace will kick off by its self.
grayfurnaceman Just a follow up. It was both the limit and the fan switch. I just touched the back of the limit switch and it reset, but the fan switch I had to remove and tap on my counter top. When the build up/corrosion? all fell out I put it back on and it works like new. I'm sure its not like new but its working correctly now. Thanks for your help. Saved me a lot of money! and subbed. Looking forward to the homemade beer! You gonna have to do some taste test if you haven't.
Hey brother; i have one of the other honeywell switches you posted with and set with the temps you said etc. The problem is it's shutting the burner off after 90 seconds.. runs just like the one in this video with no fan.. cept my fan is on and it reaches the too hot level and kicks burner off for like 6 minutes as it cools.. repeats. single digit temps in PA and thermostat reading 62° inside.. probably colder. Would imbalance of ductwork cause this (not enough return) or need bigger motor for hamster fan? Or...?
grayfurnaceman Welp.. wouldn't ya know.. the hamster wheel was spinning in the wrong direction.. reversed motor and heat pumping. Thanks to your videos!
hello gary hope to get your reply . i have a heil 7000 furnace that i will be buying a new furnace but due to medical issues i have to wait till next year . model nugk100dh12 1990 serial l935012658. my question is i need a new fan control swithc have it the exact sixe of that model i can not find a number on part i have and they dont make them it is 80,000 btu . is there a universal one i can buy for cheap or a used model i could look up just to get threw a few new york weather months. thank you Kristy
@@x.y.8581 it was the fan control i replaced it with a good guess and your video . quick question on the control moduel what should the two knobs be set at one says time on one says time off
Here is a question, last weekend my furnace started short cycling, Call the gas company because I have a repair contract with them.. they replaced the limit switch, but didn't fix the problem, saying it's the "extreme cold" they made an adjustment to the temp pins, that got me through the week, the tech told me to adjust the pins back to where they are suppose to be when it gets warmer. So I did that this morning.. same short cycling issue.. Now they I watch this video, I noticed my switch isn't working like that.. it goes on at 100, fan kicks in at 150, then it goes back to 100 and shuts off.. why would it doe that?
What is happening is that the cold air in the return is "shocking" the switch and shutting down the fan. There are a couple of reasons for that. One, if you have a very low return air temperature it could happen. Also, some fan switches have a small heater that preheats the fan switch. If that heater is failed, it may also shut off. I have a video scheduled to come out at the end of Jan covering this heater. Hope this helps. GFM
grayfurnaceman My return air is in my house, very short return.. it's a condo actually. the return length is about a foot and a half, with the furnace in an outside closet. I've been here since feb of last year and never had an issue. that's why it's confusing to me. and today, it's 62* vs the -20 it was the other day.
joey197777 My guess is the problem is outside air is getting to the furnace. There is really nothing I can see to fix this. Do not cover any outside air grilles. GFM
On some older furnaces, the limit switch opened the high voltage circuit to the transformer. So power was run to the limit in the same circuit as the was used for the fan. Hope this helps. GFM
Hi Grafurnaceman , The Lennox gas heater rooftop fan control has two extra wires go in to Fan control /high limit switch . What is these wires functioned . What can I do if I can not find the orinal part. Do I need to modify it some how . Thanks
quang nguyen They are probably a preheater. You can replace it with one without the preheater and hope it does not short cycle. Sometimes, if you set the on and off temps a little farther apart, it may work ok. This video may help: ua-cam.com/video/-0CIsqw3HRcG/v-deo.htmlFM
grayfurnaceman Hello ... I have one of those switch and I think it is bad. When I hit the manual switch the blower does not come on. I was trying to use the blower to push cool air up from the basement and it didn't come on. I check for voltage to the blower motor and I didn't get 120 volt reading. Correct me if I am wrong, but the blower motor should come on when the manual switch is turn on. I know the furnace is getting power because I can hear it come on. So do you think my switch is bad? Thank you for your time.
grayfurnaceman Thank you sir for your quick response. I ordered a replacement part from ebay. I made sure I got the same length which was 11.5". Hopefully this will allow my blower to turn on.
grayfurnaceman I replaced the fan and my blower still won't come on, but I am getting power to the motor this time. Is the motor bad or am I missing something??
Thanks, mine is almost identical but was a L4064e2544. According to honeywell, you should be able to replace it with a generic model L4064B2228 (Replaces L4064A, B and E). Going to try it out this weekend. Thanks again for the videos, they're great.
@@grayfurnaceman Really? Great, tx. You know, I had no problem, just trying to figure something out. I'm not sure how to take your response but it seems pretty cheeky and sarcastic. Why don't you watch your own video again and tell me if a person should be able to know where those 2 red wires are coming from. Or which is +/-
@@blackopal3138 It was not meant that way. Watch the video at about :30 seconds in and you can see the diagram on the switch. This equipment is AC, so there is no + or -. GFM
@@grayfurnaceman k, sorry. hate written communication. tx.... I guess what I meant for the +/- is that both wires are red so I couldn't tell which was the live (I call that +, maybe that's incorrect and misleading)
@@electriccar3253 on the video there is 2 red wire is fan, and 2 black is limit , do u mean get a jumper connect black to black? and it will by pass the limit ?
Bryce Katzman 3 minutes ago Hello! Great video! Question: I just replaced the belt drive blower motor with one that is basically the same (1/3 horsepower, 1725RPM, etc..) the problem with the switch above is: that after kicking on the motor at 150F it starts to go backwards until it hits 90F and shuts off. This takes about 5-10 minutes. If I left it like this it would do it forever. Any suggestions? Thanks for any advice. Bryce
@@grayfurnaceman - Thanks for the info. It helped a lot! - It turns out that I had some cold air escaping from an exhaust vent for a gas fireplace that I was using temporarily while my blower motor was busted. Once I closed it all was good! Thanks for the reply. I appreciate it!
Here is what it looks like. There are one on each side and I dont know how to test. black and red go up on right bar and the blue goes on the left bar. Then there is a black jumper that connects the two. www.bestbuyheatingandairconditioning.com/Merchant2/merchant.mvc?Session_ID=69df4affdab364afd51b98172e3ac67f&Store_Code=BB&Screen=PROD&Category_Code=fl-tdl&Product_Code=LIM7581
Im in a apartment , and landlord is up in age and clueless on repair... But my fan runs sometimes long time,, but after it does shut off ,, it will then keep coming on and off constantly.. So i figured i start with this but when i look up part numbers they all show one's that have a cover on them and mine does not.. Here is number i see on mine. L4064A 1347 5
The cover is not important. If there are 5 or 6 wires coming to the switch, and in the center of the switch there are 2 terminals close together with wires (usually yellow) connected, you have a fan switch that has a preheater. You can remove and isolate the wires to test if it stops. If it does stop just leave the wires isolated. GFM
@@grayfurnaceman Mine is a little like yours in pic but with 4 black wires...And on my fan switch between those 2 wires that are closer together it says remove for low voltage... I tried my best to find cross ref for newest unit to replace my part number of L4064A 1347 , and new seems to be part number L4064B 2236 which i ordered. Also the New part has a Man or Auto button on it, which my old one does not So since furnace is old i went ahead and ordered new switch which will be here in few days.. As of right now after furnace runs it will shut off, then few min later blower fan keeps coming on for aprox 3 seconds then shuts off and then back on again and it does this until it has cooled furnace enough. I've watched the round dial on the switch and its not smooth with its movement, as it jumps a little like its sticking maybe but im not sure how smooth they suppose to operate while heating up or cooling down. There may be a second issue as of a few hours ago,, as furnace went to run by turning on blower and it makes is a loud click and then motor just hums like its frozen up.... Possibly bad blower ?
@@TheC5corvette You can try separating the on and off tabs a bit more. The operation should not be smooth. There is resistance in the switch. On the motor, hit it with a small hammer. If it starts, the centrifugal switch is failing. Means the motor must be replaced. GFM
Why are you trying to fix the problem when it is the landlord's responsibility? Stop paying rent until he gets it fixed by a qualified furnace repairman!
This unit has been used for the past 50 years and this is one of the best videos I have ever seen - THANKS!!!
PS. only video that talks about the "power jumper" AND all of the limit settings.
- fact is if you are replacing the unit and have 4 total wires you should "break the jumper" and if you have 3 wires (120v both sides) you need to LEAVE the jumper. The missing wire will be on EITHER side of the jumper! Like he says, running 120VAC into the 24vDC circuit will be very exciting!
wtf?? I have 6 wires! 2 from city power, 2 from the switch transformer transformer and 2 from fan, lol The only way I see it going is 2 wires sharing a single socket, but that is not pictured. If I do what I see, wire 2 lines from city power direct to box on fan side and 2 wires from the transformer direct to box on switch side, then how does the fan work when it's not hooked up?
This comment helped me see the primary concern. 3 wires = high voltage, 4 wires = low voltage
That fan and limit switch was the most common type of fan switch used on most oil, gas, and some electric furnaces. Thanks for the comment.
GFM
My furnace is a comfortmaker and It's a 1980 style, it quit turning turning the fan on last year. I didn't know they had these things in them. The fan would stay on and the burner would kick out. Last year though the fan switch wouldn't come on and neither would the fan when it warmed up. You have turn the blower to on before it does. So I reprogrammed the thermostat to the a.c. side to operate the furnace. The furnace still cut off at the certain temperature. I had to adjust the burner. They said it on web it should burn an inch flame. It does better.
Because that strip in limit switch I lost my job .
But since i watched your videos;I really got interested in HVAC ;
Please continue .
Lennox Pluse (10/1987) G1404/5-100-6 still chuging along. Replace flapper about every 4 years. Had to change Fan Limit switch - HOWEVER generic limit switch cause Blower to short cycle. So had to add Delay -Off-Relay set to 4 minutes (that feature was built into original fan limit switch).
Sorry, your message was in the spam. The motor probably went off on overload. Most of these are automatic reset. If it does not reset after approx 1 hour, look for a reset button (probably red) and push it. If the fan will turn easily and still wont start, manually turn the fan with the power on. If the unit starts (keep your hand free), the capacitor has probably failed. If it is stiff, look for oilers over each bearing. Hope this helps.
GFM
Great job explaining the fan and limit switch! I just love and appreciate your videos. Thanks for sharing.
I have a 40 year old Lennox furnace, and my fan won't automatically shut off when
the burners shut down. I tapped on that dial on the fan and limit switch and the fan
then would shut off. When I did that, the dial turned slightly and the fan shut off.
I replaced the fan motor a couple of years ago. I did have a very dirty air filter but
replacing the filter didn't help fix the fan and limit switch. I'll probably replace my furnace
next year. Good video.
That is the classic symptom of a fan and limit failure.
GFM
What is a "fan and limit" failure? Will replacing this switch probably solve my problem? I'm guessing that it does. I just ordered a new one and will
replace it soon.
Assuming your description of the symptoms is accurate, yes.
GFM
I just replaced my fan limit switch. It was pretty easy to do. The coil
in my old limit switch was distorted and rubbing against the tube, which
is why it wouldn't rotate back to the "fan off" position when it cooled down.
Yes, I did remove the copper strip. Furnace fan is working normally now.
Thanks for the great lesson and tips.
It wasn't as cheap as I thought it would be, but I saved a lot of money
by replacing it myself (about $120 for the switch).
Thanks for the support.
GFM
Happy Thanksgiving GFM. You have been a such great instructor. I get up every morning before start working I watch your videos then go to a service.
Guy
Best Air Chicago Inc.
just finished following tip to tap duct work beside switch worked like a charm shut the breaker off first . think i will check furnace come spring .THANK YOU
Happy thanksgiving back. Its nice to know it helps.
GFM
This is exactly the switch I have and need to understand. Thank you so much.
Welcome
GFM
I have a followup question. I'm looking for a complete explanation of the whole cycle from turning up the thermostat to the burner and blower fan turning on and off. Do you have a video of that? What part exactly turns the burner on and off and the blower on and off?
I did a set of videos on what I call the "antique furnace" that may help. I don't know the age of your furnace, but most of these furnaces used the thermostat to energize the gas valve which started the burners. As the heat exchanger warmed, the heat operated fan switch (the one you have) closed and started the fan. Hope this helps.
GFM
just a note to day you explained it well and I fixed problem w/ your assistance.
Thank you SIR!!!!!!!!
Welcome
GFM
as always top of the line teaching, thank you much for that
+purrungas2012 Welcome
GFM
If your switch looks like the one in the video, remove it and look at the probe. It comes in 5", 8", and 11 1/2". Get the right length or it may not sense right. 2 ways you can get one are internet parts houses, (I dont recommend any of them, nothing negative just no experience). You may also buy from a local service repair company over the counter. Hope this helps.
GFM
If the motor was hot and now is cool, the motor is probably failed. When a fan motor gets stiff bearings, the bearings are damaged and will probably not last long anyway. Looks like a new motor. Good luck
GFM
If the limit controls the primary (120v) of the transformer, the jumper must be left in, as it is the voltage source for both the fan motor and the transformer. Hope this helps.
GFM
Thank you. I neglected to take out the jumper and the fan ran all the time.
Extremely helpful. Thank you!
hey, your videos are great and very informative, keep them coming, there are really helping me! thanks
The fan and limit for that unit does have a single pole double throw switch on the fan portion of the fan and limit. So it is special.
The general replacement ones that I have seen all have the copper jumper. Happy Thanksgiving
GFM
I have one of these on an old Rheem furnace and I can't understand why its wired like it is. The 24V red wire leaves the limit switch and goes strait to Position #1 of the Honeywell s86F intermittent igniter where I am currently missing my 24V signal to turn the GV on.
The 24V yellow lead goes from the fan limit strait to the safety switch on the main blower unit, through that and back to terminal Y.
That doesn't make any since whatsoever to me but that's the way I found it.
As always the coldest day of the year the heat quit working and has not worked since.
I have drawn up a schematic of the entire system like I found it.
Excellent video GFM thank you for sharing!!!!!
Thank you Grayfurnace man. I really appreciate that you took the time to document some of your learnings. I have been trying to assist my brother with his Honeywell Limit switch that you appear to be very familiar with. The original part is a L4064T2481 which is not produced anylonger. I have been researching and I believe the replacement should be L4064B2210 . This one seems to be general replacement. The original unit has two low voltage connections in the middle. In reviewing your Honeywell video you mention the replacment and the fact that you would need to remove the copper strip.
Can you confirm that the L4064B2210 is the part we need?, and that we will need to remove the copper strip? I appreciate your time and knowledge..
The original part had a helper heater to keep it from short cycling. The part number you have is the proper one if the insertion is 11.5 inches. It may short cycle once before it stays on but there is nothing you can do about that other than separate the on-off temps farther. The copper strip must be removed if the limit switch is in the low voltage circuit. Hope this helps.
GFM
Love your videos!! They sure save a working man a lot of money and pain!! Wondering if you can help me. I have a 30 year old Lennox furnace. This morning, the furnace ran as normal and then shut down as normal. A few minutes later, the fan restarted for a few seconds. I went inside and adjusted the 'off' switch to 110 from 100 and it seems to be okay. Initially I had changed it from 100 to 90, and found it cycled again very quickly. So I decided that was the wrong way to adjust it. So, as I said, I moved it to about 110 and it seems okay. Is this a safe thing to do? Is there something else that can be causing this secondary cycling?
+J S No problem with what you did. The short cycle of the fan is just removing any heat left in the furnace. Hope this helps.
GFM
Great explanation.
I have a honeywell fan (model # 14F0) that stopped spinning. You would hear a buzzing sound (which indicates that its motor is trying to spin but is somehow jammed) but no action. Normally this would be an easy fix, open it & lube it. The problem is I forgot to turn it off when it did that. Since the motor was on but it wasn't spinning, I think something shorted in there. So now when I turn it on there is no buzzing sound or any thing that indicates that electricity is running through it.
Excellent video explaining how this works thank you. I have a Magic Chef furnace that must have gotten an electronic ignition at some point in it's life. The pilot turns on, flame sensor is good, but the main gas valve only opened one time during troubleshooting and I never got the fan at all. Going to check the limit switch out tomorrow, curious if it has failed and cut power to the main gas valve and fan, though I am not sure why the pilot and ignitor stays on in this scenario. Hoping this understanding helps me figure it now now that I know there is more to the circuit than just the flame sensor and valve.
The other working furnace shuts down everything when heat shuts off but this must turn the fan on when the still hit burner heats it up again, the gas stays off but the fan comes on again a minute or so after the gas shuts off and then runs for a minute or so until that switch cools down.
If your ignition lights the pilot, then main gas comes on and your situation is the pilot lights but no main gas, clean the flame rod with sandpaper(it is a metal rod about 1/8" diameter in the pilot flame).
If that does not help, the ignition control has failed.
GFM
@@grayfurnaceman thank you. I cleaned the flame rod first pass but only had cloth. Swapped the whole assembly from a working unit, same thing. Today I cleaned the rod with wire brush and the burner to gas line contact points so they all bonded. I had mixed results with meter yesterday trying to find clean ground. Pilot lights and pulses no main valve fire.
I reached in and touched the pilot shroud with a screwdriver and it lit right up. Ran for a while then when back to igniting with just a pilot. Got the idea to clean the shroud, to help the ionization? Maybe the screwdriver close to the flame acted like an antenna for electrons? Cleaning the shroud in place worked great, tested on and off and a cold start 8 times. Gas company came out at my request, supposed to be 7wc and it was 6 and they adjusted as I was leaving. An hr later, same deal no fire.
Went back tonight with contact cleaner for the spade connectors and a plan to clean up the corrosion I noticed between the pilot shroud and the main assembly. Thinking about poor ionization/detection/movement of electrons again. I also cleaned the pilot gas line, the end was dirty and I accidentally made it worse, was able to clean with contact cleaner and a single fine bristle of steel brush thru the tiny orifices. Blew thru it, cleaned the heck out of the whole igniter/pilot/flame rod assembly and their contact points to the burner. Fired right up. I removed the igniter to check the pilot without full gas and it still pulses but it's blue now without a yellow tip. Even with gas on high the flame rod doesn't get red hot anymore and it stays lit consistently and lights instantly after the pilot. I know now it's not the heat I need like a thermocouple would function but rather the ionization in the flame.
I think the rod was fine but whatever magic happens with the ionization wasn't happening due to poor flame generation by the pilot and bad electrical continuity between components. Maybe the contact cleaner on the spade connectors helped too.
I appreciate your videos that helped me catch up on how various components worked. The most important thing was the difference between a flame rod and thermocouple. Once I understood the operation I could make sure the best conditions existed.
Hoping it holds up. I think I have finally seen how it's supposed to work and what a good pilot and flame rod activation looks like.
The lesson I already knew but was too rushed to bother to do first this time was to clean while I work. No matter what it is you are working on, dirt, corrosion, dust, it all gets in the way of good operation. I wanted it to work first before I bothered cleaning, big mistake.
Also based on your videos I understand my limit switch now. It was all high voltage and if it cuts off it would kill the power to the transformer too. It controls the fan independent of the gas valve operation only responding to the temperature of the heat exchanger. I never got fan because I never reached temperature.
Its a Rheem/Ruud RGDA model.
GFM
Hi, I have a lenox pulse and the controller is g891tca-8103. It runs fine sometimes for a week or two then shuts off. The green light on the controller goes out as well. Then I shut breaker on and off and it works fine for a week or two. I have cleaned the blower, bottom of the heat exchanger, new filter, and had the board replaced. Flame sensor and spark plug were also cleaned. Have you run across this problem? Now I was thinking if it had anything to do with this limit switch. Any help would be appreciated.
Thanks. Unfortunately it does not reset on its own and there is no reset button. Pushing the fan manually wont work either. I think something shorted out, because the fan was too stiff to spin while the power was left on.
I would try adjusting first. Look at the playlist on my channel "furnace fan switches" Hope this helps.
Hello. I have a question that is not related to this video, but I thought to ask since this is a field that you are knowledgeable about. The question will be in the next comment because wouldn't fit here.
So I did one of these today but on a Miller furnace I replaced it the exactly the same wires and everything and for some reason the wires got burned towards the fan and started arcing ugh!
OK took off the limit switch and just pressed at the back of it and the one on the right clicked back in? I hope that makes sense. I put it back on and wired it and it started!!! So it is the limit switch. I'm not sure that fixed it though. I have heat at least. BUT it ran for a minute and the fan never came on? Not sure why I turned the fan on manually and the furnace came back on? I'm going to put it back on auto to see if it works by its self.
This may be a dumb question but is there anyway to know what wires are what coming out of the furnace to connect to this switch? The person who tried to replace the switch on mine did not make note of what wire went where before taking it out and the wire colors don't match 😑
There are many different ways to wire that switch. You will probably need to get a professional on it.
GFM
A couple questions. First of all, on a millivolt system, this is also wired to shut off the gas valve, if the fan doesn't come on (e.g., a power outage)? Second, I notice that a few people here have had issues with these units sticking. What is the lifespan of these units, and would it be prudent to replace them on an old furnace BEFORE failure?
Yes there is an overtemp limit. I have found these fan and limit switches to be dependable and most last the life of the furnace.
GFM
What part did you use to replace that switch? I have one like this but can't seem to find a replacement with the same part number. It looks identical. Has a 5 inch probe.
Excellent !!! Thanks for the help
Welcome
GFM
Great tip, i ran into a stuck two stage limit on a icp oil furnace, i bumped it to get it going but just replaces it with a oem part what is the difference besides a 4 day wait from the parts house? And one more thing, how do you know which limits are just 120 and which ones are 120/24, is it on the package? or are they all 120 and you break the copper peice
Hi Grayfurnaceman. You are the man with the answers so I hope it's ok for me to ask also. My neighbor's central furnace lights just fine and the fan comes on for 2 seconds off a split second then on for 3 and so on long and longer for maybe 5 times within 30 seconds then stays on fine and runs fine and cycles off fine. She said it's always done that so probably many years. Mine did that also before I changed my central ac/heat system. Could this be the fan limit switch being faulty?
If your fan and limit is adjustable, the on and off time can be separated until it no longer short cycles.
GFM
What is the proper way to recalibrate those switches? Mine was reading about -200 deg F at about 60 deg F. We heated it with a small propane torch to about 500 F and I would hold the dial and pour cold water on the bi-metallic strip. We did that several times and it was close, but still reading colder than ambient temperature. I reached in to the bi-metallic strip with a pair of needle nose pliers and smashed one of the coils a slight bit to make the strip a little longer. I would guess it is within 10 deg F now.
great video...replacing the fan switch. it has the little jumper wire, how do you test to see if 24v or 120? will the two wires on the right read either one when powered up? thanks
If the original switch has the jumper, it is a 120 volt system. Hope this helps.
GFM
I might have an issue with my fan limit switch ( honeywell dial ) My compressor turns on but fan doesn't, unless I rotate the Fan Limit dial slightly, but when the compressor turns off the fan still runs. so in the summertime I just let the fan run, because the thermostat still controls the compressor. I haven't been able to find the video that supports my issue. I have a Janitrol Central Air unit. My house was built in 1986. Appreciate any suggestions. Thanks
I'm having same issue.
It appears nothing came thru. Did you send a pic?
GFM
Hi,
My Lennox G16 conservator III series natural gas furnace fan won't turn on in auto mode however it does turn on in FAN mode. I had an HVAC tech come in and diagnosed it to be bad Fan Limit Control Switch. I myself ordered a brand new Honeywell part from e-bay and replaced it.
The problem still persists...any suggestions?
Thanks
Jas
I have the same limit factory set to 170 degrees as called for for my Heil furnace. The furnace will run for several minutes and this limit will shut down the gas valve and the blower will keep running until the limit cools down and the burners will pick up again. Should I increase the limit temp, .Increase blower speed, or remove and inspect Switch is wired for limit only
Hey Jetstream, I know your post is 6 years old but my Heil gas heater is doing the same exact thing as yours. Did you ever figure your situation out? Was it a crack in your heat exchanger? Please reply if you are still alive (lol)...Thanks
Rather use that style switch then the snap switch, works better and last longer than snap.
I got this same one,my blower motor stays running ,i isolated the thermostat & still runs,i gotta turn off breaker for it to stop. Could this be the issue ,doesn't have a control board
It is probable that the switch has failed. If you strike the dial of the switch with a screwdriver and it shuts off, it has failed.
GFM
@@grayfurnaceman thanks for the quick reply, i just replaced panel door switch & still runs,it turns off when i remove bottom panel off,tstat still isolated, i also took wire off that comes from transformer i believe is the common wire that goes to capacitor & it stops,could it be transformer?
@@grayfurnaceman transformer has a plastic piece attach to it were tstat wires connect to it,maybe that could be the issue? Doesnt look like a relay that i can remove
@@grayfurnaceman its fixed i just tapped on fan limit switch & it works now
@@justdissin7340 Probably not. In most cases, it will stick again.
I have a question that hopefully you can help me with related to one of these fan/limit switches. I have a furnace in a house i purchased that short cycles it has a L4064y that does not seem to have the limit switch adjusting tab above the break @ 150* the problem i am having with this is that when the thermal coil trips the fan switch it pops the high limit and cuts the gas valve also causing a short cycle condition. the installation instructions for the 4064y say that it is suppposed to use the 24v hooked to an internal heater to controll fan on. it is not hooked up in this manner on the furnace. my question does is this switch defective or broken missing the adjusting tab for limit or do some just have a fixed limit that is not adjustable so it doesnt have a tab. and would not having the 24v hooked to the heater cause the limit to trip prematurely? Thanks for your time and consideration
Is this fixable? If so, how? Thanks.
hello
i have a valley comfort wood/electric combo
i have watched your videos on adjusting the 3 point for the kick in and off
but this fan keeps staying on for ever. it doesn't stop for 20-30 mins
whats the deal
thanks Sr
My furnace runs about 90sec before forced air fan starts later when all is off ..the fan comes back on about 2 min later for 30seconds .its a 10yr old big furnace with 1.6gph nozzle does this seem normal...seems to run to long before fan starts.
VN Dustoff If your furnace uses a fan switch like the one in the video, the on and off temps are adjustable. Off can be set at 90 to 100 and on at 130 to 140. Set them farther to eliminate the short cycle after burner shutdown.
GFM
Thanks Grayfurnaceman, good video. Hopefully you can solve my problem. I have a 25 year old Rheem Horizontal Furnace. The fan no longer turns off, it continually runs, the thermostat is set to auto and is working correctly, we believe the Fan limit Switch is the problem. The existing switch is a 6 wire switch, Honeywell model L4064T1897, it is no longer manufactured. We can only find 4 wire replacement switches. Can we use a 4 wire replacement switch, if yes, what do we do with the 2 wires not being used any longer, and what is the purpose of those two wires? Thanks!
The 4 wire should work ok. Isolate the wires. Use a wire nut on each. They power a small heater in the switch to avoid short cycling of the fan.
GFM
Thanks, do you know of any 6 wire replacement switches?
Mine doesn't turn the fan on either. I had to program my thermostat to turn it on. 😒
so is this a faulty switch since it would not kick the blower on. I am having the same problem.
I have a question for you: my furnace has this type of old honeywell limit switch. The problem is, sometimes after the furnace has run for a long time, the actual switch sticks and won't turn the blower off. I occasionally have to turn the power off and back on to get the blower to stop running. Can these older type limit switches be replaced or fixed? Thanks!
Very common problem. Just to make sure, hit the side of the ductwork near the switch when it sticks on. If it shuts down, the switch is sticking. You can get the switch from internet sources and HVAC dealers.
GFM
grayfurnaceman
Thanks for the quick response! the problem usually occurs after the furnace has run for a while. I have the thermostat to go from 66 degrees at night to 68 when I get up, and that results in the furnace running for about 15 minutes (the burner). the fan will then stay on for an extra 5 to 10 minutes usually. If the furnace comes on just to maintain a given temp for say, 5 minutes, the fan will then stay on for about a minute. Does that still sound like the fan switch? I don't think there are any blockages in the ductwork and the filter is brand new. Thanks for your help.
***** It depends on the type of furnace. A very old oil fired furnace may run much longer because the heat exchanger is much more massive. Newer ones will shut down in 2 to 5 minutes. You can test this if you place a temp probe in the duct (it must be placed in one of the ducts 2-3 feet from the furnace). Hope this helps.
GFM
grayfurnaceman
Thanks again! I think I'll just call a service company and get it looked at to be safe. It's been a long time since it's been looked at. I do appreciate the info though.
grayfurnaceman I have one like that and it sticks also. I can barely,barely tap the dial and it shuts off fan. Can this be cleaned or repaired? If not, about how much do they cost? Thanks for any help!
Strange.. The NEC states that High and low voltage cant be in the same box without separation.
Except for manufacturer's instructions.
GFM
I have an old octopus furnace with a honeywell la412a16x- - 2? I cannot find this part anywhere. Is there a recommended replacement for this?
You can try this one: Honeywell L4064B2236. Use the same probe length as the original.
GFM
@@grayfurnaceman thanks i appreciate it.
I am confused. What did not come through? Send a pic of what?
If you mean my question did not come through, it is there in the full comments. Just to be sure I'll post it again. Thanks.
That was so helpful thanks
Welcome
GFM
I would like to add a single pole switch to turn on my furnace air blower, to use as a summer fan to bring cold air from the basement. My fan limit control (white-rodgers) has a manual switch to turn on the fan, but I want to install a switch on the first floor near my thermostat so i don't have to go to the basement to turn it on. I assume the switch can be installed branching off of the fan side terminals of the limit switch. The switch receives 120v both sides and not 24vac. Would this be something that would be safe to do ?
It is done all the time. Just wire it in parallel to the fan switch. Hope this helps.
GFM
I just got the same furnace as that today it has a limit switch to later ill video it check it out on my account
So question here, this limit switch will not allow the furnace blower to turn on unless the gas/oil is lit? You can't just run the fan by itself?
If your furnace is equipped with this switch, there may be a white button on the left side of the switch. When pushed in, it will turn on the fan without the burners.
Additionally, you may have a fan center on the furnace that will allow the thermostat to turn on the fan only.
GFM
@@grayfurnaceman Thanks man!
This switch is exactly like mine. My question is about the manual fan "push/pull" did they just leave it off? Is there a plastic pin that needs to be put in it? It appears to just be a hole.
The manual fan switch is an option. Many of these switches do not come with it.
GFM
Thank you so much! I set mine to start the fan at a lower temperature and runto a a much lower temp and I'm happy with that!
I need to know if that switch has anything to do with the burner cutting off ? It will run for a while then cuts off no gas seems to be getting to it? The Polit will light I can hear the valve clicking, The burner will light sometimes and sometimes not, if not it will cycle out. When it does light a lot of times the flame is pulsating then level out. It will run for sometimes 10 mins then cuts off, trys to light back sometimes it will and sometimes it won't. I do not see any pressure switches or flame indicator, could this be the gas value? or limit control?
UPDATE- I removed the metal shield behind the gas valve between the burners and gas valve and it is working, I put the shield back on and it cuts off? Maybe it's the burner not getting enough o2?
barb carsner Give me a Maker and model#
GFM
How do I tell if the limit switch is bad? Switch looks just like one in video, on a 16-17 year old propane Amana. Burner starts and as temp gets up the blower starts and runs 30-60 second and blower cuts off. Burner continues and switch turns blower back on for a minute or so... then off. If the house is doing a big warmup the burner keeps going but the blower keeps cycling like this. Replace switch or can an adjustment do it?
Tom Long It sounds like the on and off temps are too close. Try this video: ua-cam.com/video/QpHfFdk04u0/v-deo.html Hope it helps.
GFM
grayfurnaceman thanks for your quick reply and your helpful videos. I actually found that video shortly after I posted the question. Yes, the on and off were 20-25° difference. Now I have them approx 100 and 140. I also found the old install manual and it said "set to factory defaults" but didn't bother to say what they are. Guess things can get out of whack--this setting seemed to change on its own--working right and then I started noticing the blower cycling off and on too often.
very good video you can help me I have a problem with my heater tries to turn it on but it sends me the sign of limited swint combustion fallen open I replaced it with a new one but it remains the same if you can help me
I am not sure if I am understanding you right. Are you saying your furnace shuts off the burner because it is too hot and you have replaced the combination fan and limit? It would also help if I knew the fuel used in the furnace and an approximate age.
GFM
I am confused what then is rollout switch use for my fan kept running after furnace shut off and never stopped when I went done to check I tapped the limit rollout switch with screw driver and it turned off is this possible
When the limit is open, the fan stays on because the furnace thinks it is too hot. My thought is you have a low airflow problem. Possible dirty filter. If the switch shuts off often, it sometimes will stick open. When you hit it, it broke it loose. Replace the switch and find the low airflow problem.
GFM
Did Richard hook something up wrong?
I have an old rheem furnace from around 1978 or 1979, at one point the furnace was short cycling I think. The fan would come on again for a short time after it had already shut off, someone adjusted it and that stopped. Anyway, now the fan will occasionally keep running after the flame is off, never turning off. Could it be this, or is there a separate fan relay that is sticking. When it happens, if I tap the side of the furnace the fan will shut off.
The fan switch has failed. About time.
GFM
Thankyou, I appreciate the help.
I have another question. So, the furnace is a Rheem RGMA-080A Furnace. Should I invest money in repairing it? Or should I replace it? I haven't been able to figure out which fan switch goes in it.
At this point, I would replace. Sometimes you have to give up. Newer ones will have higher efficiency.
GFM
Hi Gray, last year at the end of winter my limit switch was replaced along with the thermostat. Now Fall is here, I turn it on and it worked fine. The second time it never worked again.. The fan will come on if I turn it to ON, but the burners never light up. The pilot light is lit and stays on... Any further suggestions in what to do? Thanks, Scott
Scotty E. Look for voltage to the gas valve. Voltage there valve is not opening. No voltage, bypass the thermostat with a jumper. Hope this helps.
GFM
grayfurnaceman Thanks Gray, I Finally was able to look at this again. I'm not sure how to check the voltage on the gas valve, but I did go ahead and bypass the thermostat and still nothing. I even switched thermostats with the good on, still nothing.. On auto the fan doesn't ever kick in. Of course if you just turn it to on, the fan kicks in, but the burners never light up... Anything else I can check? Thanks!
I have a bad limit switch(open). It's a old ge furnace. I can't find the part. What options do I have?
If you can send me pics, I may be able to help. Send to Grayfurnaceman@gmail.com
GFM
@@grayfurnaceman thanks, I'll take some pictures and send them.
I sent the pictures
What model is that furnace i think it is the same as mine?
Also would my old furnace have a capacitor? And if it does where would something like that be located?
+Mike LikesBeer Just saw this one. Most of them do. They are located either on the blower housing or in the wiring connection box.
GFM
Does the jumper need to be there if the limit is going to a step down transformer? Thanx
I hope you got an answer after 7 years but yes. The jumper distributes 120 to both the fan and the limit circuits... look for 3 wires at the control and the limit protection is likely on the primary side of the transformer. If the jumper isn't there or broken off... look for 4 wires and the limit protection is likely on the secondary or 24 volt side of the transfirmer.
In either case interrupting power disables the gas valve and shuts off the burners until limit resets after cooling.
Hi Gray,
I have a ICP PGAA24C1K1 unit. Unit turns on for 5 minutes and cycles off for 2 minutes. Keeps repeating at those intervals. Me and a tech narrowed it to to either the pressure switch, hi limit switch or the fan control switch. The high limit switch is not easily accessible. I live at 5300 feet above sea level. some say pressure switch might cause issues at this elevation. Any suggestions. Thanks
My guess is the limit is cutting off. It is probably doing its job. I would be looking for air flow problems, such as dirty blower or plugged filter. There could also be a crack in the heat exchanger near the limit. The pressure switch will usually not work at all if it is failed. Hope this helps.
GFM
grayfurnaceman Thanks Gray. Will look into that and let you know what I find.
Ok it ain't broke technology so don't fix it but is there is a 21st centurary off the shelf replacement for this mechincal bimetal device? Thx! I knew nothing about oil furnances a few days ago but I am an experienced smart devices maker and engineer. It just seems to me that we can upgrade our decades old furnances without replacing the whole thing. I was pondering using a onewire 18B20 temp probe and a mini brain (e.g. arduino) plus couple relays for the oil burner and blower. Then one could tweek the on-off-over termpature settings and see actual temperatures on (via bluetooth and wifi) a smartphone. I'd throw in some other temperature probes for the burn chamber and maybe the exhaust gas. How about a probes for flue and chamber vaccum, could even have it control the manifold weight. How about a CO detector too. All that can be controller by one little brain. You can even have a simple display and control buttons so as to not require a phone or any wireless connection. But with wifi connection the ower can monitor health of the furnance and be alerted about issues long before they become trouble or dangerous.
I have a Lennox pulse g14. Has no problem heating the house however the fan will turn on and off several times after the heating cycle is satisfied. I adjusted the fan off setting to below 90 degrees and now it only comes on once after the heating cycle. But as soon as the fan shuts off it slowly rotates back to 140 and stays there. The current fan limit switch is a honeywell l4064t2242 it says this part is discontinued do you know which one I can replace it with?
I believe the replacement fan switch simply does not have a preheater installed. Use the same length probe and you should be ok.
GFM
Ok. I have 6 total wires going into my switch does that seem right?
@@daltongavers491 Yes. The 2 center wires are for the preheater. Just isolate them.
GFM
@@grayfurnaceman7640 changed out the fan/limit switch, works great but while I was working on it I found a small propane leak around the top of the gas valve. I dont know If it's the pipes or the gas valve itself. If I shut off the gas to the furnace disconnect the pipes and put thread compound on them and reconnect them with I have to do anything special to light my furnace again? Or should it just resume like normal
@@daltongavers491 First, I would try to isolate the leak by using a soap solution on all fittings.
Once it is reassembled, you can just fire it off. It may safety out for the first couple of ignition tries, but it should fire off ok.
GFM
I replaced the switch, cut the jumper tab, but now the furnace blower fan will not shutoff. It fixed the problem where the blower fan would not turn on. Any ideas? set to 100 120 200
haha there is a white manual override button, pulled out, all good
If your manual button is pulled out, try 110, 140.
GFM
@@grayfurnaceman thanks, is that the proper settings? 110 140?
@@DreadPiratePain Generally, yes.
GFM
Can I connect a thermostat to this limit switch to control the temperature to control the temperature in another room I have one on a wood burner
It would only shut off the fan if it exceeds the high temp. I can't see a use for it.
GFM
So once the high limit is reached and power is turned off to the gas valve , at what temperature will the power be restored to the gas valve?
You said they dont use these anymore....what do they use now?
Usually, about 180F. Newer furnaces turn on and off the fan with a timer. The fan is also turned on if the temperature of the airflow exceeds a preset temp very similar to the honeywell fan and limit.
GFM
So if the limit switch is set to 200, the power will be cut off and then come back on at 180?
Approximately, yes.
GFM
I got one more question. I replaced my thermostat and the AC comes on fine and the fan comes on fine. I think my limit control switch might be bad. The thing is I don't know how to test it and mine is not like this one. Mine are two bars laying in parallel beside each other. There is a red black and blue wire. Can I put any limit switch on it or do I have to replace it with the same one? Fanomatic or something like that. And can you tell me how I could test that limit?
+Mike LikesBeer Sorry it is a thermo disc
+Mike LikesBeer They are specific to each furnace model.
GFM
grayfurnaceman Thats what the problem was the whole time. There are two on this one. I think one is working know and the other is still not functioning right because its not kicking the fan on. Because the fan wont kick on unless you turn it on manually the furnace will kick off by its self.
grayfurnaceman Just a follow up. It was both the limit and the fan switch. I just touched the back of the limit switch and it reset, but the fan switch I had to remove and tap on my counter top. When the build up/corrosion? all fell out I put it back on and it works like new. I'm sure its not like new but its working correctly now.
Thanks for your help. Saved me a lot of money! and subbed. Looking forward to the homemade beer! You gonna have to do some taste test if you haven't.
+Mike LikesBeer The switch will probably fail again. But, who knows. The taste test are coming and maybe some recipes if I get a really good one.
GFM
Hey brother; i have one of the other honeywell switches you posted with and set with the temps you said etc. The problem is it's shutting the burner off after 90 seconds.. runs just like the one in this video with no fan.. cept my fan is on and it reaches the too hot level and kicks burner off for like 6 minutes as it cools.. repeats. single digit temps in PA and thermostat reading 62° inside.. probably colder. Would imbalance of ductwork cause this (not enough return) or need bigger motor for hamster fan? Or...?
There could be ductwork problems or a crack in the heat exchanger near the fan and limit.
GFM
grayfurnaceman
Welp.. wouldn't ya know.. the hamster wheel was spinning in the wrong direction.. reversed motor and heat pumping. Thanks to your videos!
That will make a difference
GFM
I need this part for my furnace. Where can I get one?
hello gary hope to get your reply . i have a heil 7000 furnace that i will be buying a new furnace but due to medical issues i have to wait till next year . model nugk100dh12 1990 serial l935012658. my question is i need a new fan control swithc have it the exact sixe of that model i can not find a number on part i have and they dont make them it is 80,000 btu . is there a universal one i can buy for cheap or a used model i could look up just to get threw a few new york weather months. thank you Kristy
How do you know the switch is defective? Is it set correctly? What do you mean "they don't make them"?
@@x.y.8581 it was the fan control i replaced it with a good guess and your video . quick question on the control moduel what should the two knobs be set at one says time on one says time off
Here is a question, last weekend my furnace started short cycling, Call the gas company because I have a repair contract with them.. they replaced the limit switch, but didn't fix the problem, saying it's the "extreme cold" they made an adjustment to the temp pins, that got me through the week, the tech told me to adjust the pins back to where they are suppose to be when it gets warmer. So I did that this morning.. same short cycling issue.. Now they I watch this video, I noticed my switch isn't working like that.. it goes on at 100, fan kicks in at 150, then it goes back to 100 and shuts off.. why would it doe that?
What is happening is that the cold air in the return is "shocking" the switch and shutting down the fan. There are a couple of reasons for that. One, if you have a very low return air temperature it could happen. Also, some fan switches have a small heater that preheats the fan switch. If that heater is failed, it may also shut off. I have a video scheduled to come out at the end of Jan covering this heater. Hope this helps.
GFM
grayfurnaceman
My return air is in my house, very short return.. it's a condo actually. the return length is about a foot and a half, with the furnace in an outside closet. I've been here since feb of last year and never had an issue. that's why it's confusing to me. and today, it's 62* vs the -20 it was the other day.
joey197777 Your furnace is outside the house? In a lean to next the house?
GFM
it's in a closet outside. It's how the condo was built.
joey197777 My guess is the problem is outside air is getting to the furnace. There is really nothing I can see to fix this. Do not cover any outside air grilles.
GFM
Is there ever an instance where u need the little copper switch in there? If so then explain it.
On some older furnaces, the limit switch opened the high voltage circuit to the transformer. So power was run to the limit in the same circuit as the was used for the fan. Hope this helps.
GFM
that does help
hi there, please tell me where i can adjust the speed of the fan?
TimberWolvesX X First I need to know which fan.
GFM
Hi Grafurnaceman ,
The Lennox gas heater rooftop fan control has two extra wires go in to Fan control /high limit switch . What is these wires functioned . What can I do if I can not find the orinal part. Do I need to modify it some how . Thanks
quang nguyen They are probably a preheater. You can replace it with one without the preheater and hope it does not short cycle. Sometimes, if you set the on and off temps a little farther apart, it may work ok. This video may help: ua-cam.com/video/-0CIsqw3HRcG/v-deo.htmlFM
grayfurnaceman Hello ... I have one of those switch and I think it is bad. When I hit the manual switch the blower does not come on. I was trying to use the blower to push cool air up from the basement and it didn't come on. I check for voltage to the blower motor and I didn't get 120 volt reading. Correct me if I am wrong, but the blower motor should come on when the manual switch is turn on. I know the furnace is getting power because I can hear it come on. So do you think my switch is bad? Thank you for your time.
spirittoo It certainly should. The control may be failed.
GFM
grayfurnaceman Thank you sir for your quick response. I ordered a replacement part from ebay. I made sure I got the same length which was 11.5". Hopefully this will allow my blower to turn on.
grayfurnaceman I replaced the fan and my blower still won't come on, but I am getting power to the motor this time. Is the motor bad or am I missing something??
that did help
Hi, do you happen to know the model number of this limit switch off the top of your head?
There are several models that pretty much look the same from the outside. The difference is in the length of the probe. Try L4064B to start.
GFM
Thanks, mine is almost identical but was a L4064e2544. According to honeywell, you should be able to replace it with a generic model L4064B2228 (Replaces L4064A, B and E). Going to try it out this weekend. Thanks again for the videos, they're great.
I don't get it. I have exact switch but I don't see how the fan is connected??
The fan is connected thru the the contacts marked "fan" on the switch.
GFM
@@grayfurnaceman Really? Great, tx. You know, I had no problem, just trying to figure something out. I'm not sure how to take your response but it seems pretty cheeky and sarcastic. Why don't you watch your own video again and tell me if a person should be able to know where those 2 red wires are coming from. Or which is +/-
@@blackopal3138 It was not meant that way. Watch the video at about :30 seconds in and you can see the diagram on the switch. This equipment is AC, so there is no + or -.
GFM
@@grayfurnaceman k, sorry. hate written communication. tx.... I guess what I meant for the +/- is that both wires are red so I couldn't tell which was the live (I call that +, maybe that's incorrect and misleading)
Why don't you get a book on furnaces and study them rather than bothering GFM with your obscure questions?
hi ,i an new tech ,i had a furnace has problem is working heat and ac in same time ,i am looking for advice if you can thank you
***** Does the house have a whole house fan?
GFM
sorry,what you mean by gfm ,i work as maintenance in apartment complex thank you
***** Those are just my initials
GFM
sorry gfm ,what you mean by a whole house fan ?,my furnace is air forced the fan is in furnace
thank you
hi , im a new tech, , is there any way i can by pass this limit switch
You can jumper the terminals between the limit switch.
GFM
@@electriccar3253 on the video there is 2 red wire is fan, and 2 black is limit , do u mean get a jumper connect black to black? and it will by pass the limit ?
@@geniusliu143 Yes
GFM
I have one of those, what is the replacement part for it? .
Bryce Katzman
3 minutes ago
Hello! Great video! Question: I just replaced the belt drive blower motor with one that is basically the same (1/3 horsepower, 1725RPM, etc..) the problem with the switch above is: that after kicking on the motor at 150F it starts to go backwards until it hits 90F and shuts off. This takes about 5-10 minutes. If I left it like this it would do it forever. Any suggestions? Thanks for any advice. Bryce
Too much air or return air too low temp. Is the amp draw the same as the old motor?
GFM
@@grayfurnaceman - Thanks for the info. It helped a lot! - It turns out that I had some cold air escaping from an exhaust vent for a gas fireplace that I was using temporarily while my blower motor was busted. Once I closed it all was good! Thanks for the reply. I appreciate it!
great where can I pick one up
Generally, there are 2 ways to go. One, you should be able to get one from a local HVAC dealer. Two, there are a number internet sources.
could I fix the one I have if I clean it the inside probe
Generally not. You can remove it and clean the element, but it probably won't help.
GFM
I have a number its L4064E2015-6-8843N S then another number right below not sure its part of top number 025-23005
I would like to replace limit control the only number I found on the side was L4064E2015-6-8843N S025-23005 ......Honeywell
Here is what it looks like. There are one on each side and I dont know how to test. black and red go up on right bar and the blue goes on the left bar. Then there is a black jumper that connects the two.
www.bestbuyheatingandairconditioning.com/Merchant2/merchant.mvc?Session_ID=69df4affdab364afd51b98172e3ac67f&Store_Code=BB&Screen=PROD&Category_Code=fl-tdl&Product_Code=LIM7581
Im in a apartment , and landlord is up in age and clueless on repair... But my fan runs sometimes long time,, but after it does shut off ,, it will then keep coming on and off constantly..
So i figured i start with this but when i look up part numbers they all show one's that have a cover on them and mine does not.. Here is number i see on mine. L4064A 1347 5
The cover is not important. If there are 5 or 6 wires coming to the switch, and in the center of the switch there are 2 terminals close together with wires (usually yellow) connected, you have a fan switch that has a preheater. You can remove and isolate the wires to test if it stops. If it does stop just leave the wires isolated.
GFM
@@grayfurnaceman Mine is a little like yours in pic but with 4 black wires...And on my fan switch between those 2 wires that are closer together it says remove for low voltage...
I tried my best to find cross ref for newest unit to replace my part number of L4064A 1347 , and new seems to be part number L4064B 2236 which i ordered.
Also the New part has a Man or Auto button on it, which my old one does not
So since furnace is old i went ahead and ordered new switch which will be here in few days.. As of right now after furnace runs it will shut off, then few min later blower fan keeps coming on for aprox 3 seconds then shuts off and then back on again and it does this until it has cooled furnace enough.
I've watched the round dial on the switch and its not smooth with its movement, as it jumps a little like its sticking maybe but im not sure how smooth they suppose to operate while heating up or cooling down.
There may be a second issue as of a few hours ago,, as furnace went to run by turning on blower and it makes is a loud click and then motor just hums like its frozen up.... Possibly bad blower ?
@@TheC5corvette You can try separating the on and off tabs a bit more. The operation should not be smooth. There is resistance in the switch.
On the motor, hit it with a small hammer. If it starts, the centrifugal switch is failing. Means the motor must be replaced.
GFM
Why are you trying to fix the problem when it is the landlord's responsibility? Stop paying rent until he gets it fixed by a qualified furnace repairman!