HVAC Electric heat kit / strips shown!
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- Опубліковано 7 вер 2024
- Showing an electric heat kit pulled from a Goodman air handler and talking a little bit about operation and trouble shooting. I've VERY tired so apologies for lack of a better description, haven't posted anything in a while though!
REMEMBER: This video is intended for technicians and those going to school for hvac, leave testing and repair to the professionals!
IF YOU FIND THIS VIDEO USEFUL * please* feel free to make a donation! Hey, everyone likes money, right? :)
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p.s. The above link is there because I have had several people ASK for me to put it there.
Thanks for the video. I worked in HVAC in the 1980s and I've been off my tools for a while. I am trying to help out our church and they have electric heat. Your video helped me remember the circuitry. I look forward to other videos
Thanks Frank! I appreciate it!! It's always nice to get a thanks or hear how a video helped, wether just from an educational point of view, or if something got fixed.
Understand being off the tools for a while, lol, though not as long as you, hehehe! I've been out of action for quite a few years now do to spinal problems. I'm a few years out now from my last major spinal surgery, already had a good bit of steel in me, but they pretty much have everything bolted, plated, shimmed and screwed down now, lol!!
Finally feeling good enough to start working on some more videos, well after buying a new computer for Christmas! My old desktop and laptop were 8+ years old and getting long in the tooth. When the desktop finally started going south, i wringed my hands for six months comparing computers and griping on how expensive everything is, lol!
So, new laptop and i have a huge pile of old video footage on all kinds of things that needs editing and uploaded, plus a bunch of new ideas for videos! Just need to get used to Windows 10 after being on 7 for so long, learn some new editing software (ugh!) And make myself do it!
If forgot how tedious it is editing footage down, lol!!
Have a few new tool videos I have been wanting to make, so might bump those ahead of old stuff, hehe!
Hope everything goes well with the church work!! The only helping out I have like that is popping over to an old ham radio friend of mine, i think he's 90 this year, and he gets ants in his contactor every year, it seems, lol!
Take care!
Anyway, to make a short story long, yeah, I have think hard or crack out my HVAC notes that i was making on things as I worked on different things, to answer some oddball questions sometimes ;)
Thank you very much for this video. I watched it a few times and finally decided to change the sequencers. There are two and they are ganged together. I couldn't have fixed it without your help because the schematic on the furnace shows a lot of 240VAC wiring, but they only read 115VAC. Even the voltage coming into the breakers inside the furnace don't read 240VAC. The only place I found it was at the sequencer and at one set of elements. Anyway, the sequencers were the fix and I appreciate it.
Great tutorial w/fundamentals! Helped me understand my HVAC heat pump even more. I hate heat pumps for heat but great for A/C. Thanks
instablaster.
Hey John, well there is a possibility that the last time they used the heat that the heat sequencer STUCK ON and was running the heating coil constantly. The limit would cut it off and when the limit cooled the element would come back on and the cycle would continue. The melting comes in because when the Blower isn't running for the AC the heating elements are just running wild and putting stress amp loads on the wiring, hense the melting. Always fun finding an AC in summer with heat strip on!
Yes! I don't recall the amp rating on the 90-340 series but I like the small format on those. If nothing else you can stick a contactor in there! My heat here at the hosue uses contactors :>
Best video yet on this subject
Really glad u decided to do te second half of video! Learned more about how this system works from those 6 minutes than I have in the past 1.5 hours spent researching! Thanks a bunch!!!
This type of heater uses a insane amount of electric. Most places in florida has these since it does not get cold that often but when it does these thing jack the bill up big time
Just a clear picture of the wiring helps understanding what is going on. Thank you. Yes, flying saucers not made by humans are real.
Best video I've found on this.
Liked your video.Strip heat can be a problem to diagnose as you have shown.Keep those videos coming.Wish you would do one on reading a charging chart and showing how to correctly charge a heat pump in the winter.
that particular brand is expensive to repair. I have a Coleman 3500 series, and the heat strips are in pairs, so if one of the coils goes bad, its easier to replace the unit. I added 250V indicator lamps to my system to show which element is on and I have 3 lamps wired across each of the high limit switches to show trouble or over heating. adding 250V neon indicator lamps helps in showing what the unit is doing. I really love my furnace! so easy to service!
Very helpful and straight to the point
Great job. Thanks for adding the trouble shooting part to the video. It was just what I was looking for.
Thanks for this great video. Thanks for the explanation, I was able to test all my voltages and discover an open ground on the first heat sequencer coil which didn't allow the first and so the second coil to energize. Broken connector on a ground wire. Thanks again, well explained, perfect detail.
Greg Williams Costello heating and cooling installed a new furnace. They installed a Goodman mbr1200aa-1 ac, or tried to install. Very disappointed and frustrated. The owner, Gene, gave us a estimate. Then the next day had 2 young guys install the furnace. They did not know what they were doing. The job was supposed to take less than two hours. They worked from 9am to 2pm with the job not completed.
After they got "done" wiring the furnace, they flipped the Goodman breaker then flipped the main breaker.... sparked started flying, lit up the house! They wired it wrong and screwed up my new furnace.
The owner went to go get a circuit board and came back around 6pm. During that time, the Goodman was left running, blower did not shut off and the furnace heat did not shut off either. So for hours the thermostat was set at 63 degrees Fahrenheit and the temperature in the house kept raising up to 88 degrees. Unbearable and the breaker was too hot to touch to shut it off.
The owner arrived around 6pm to fix everything, the circuit board part, then realized he needs another part, a relay. Left to go get the relay, and came back around 8pm.
He got the furnace up and running on 1 element. So it didn't blow hot air, and it's 19 degrees outside! He said he would come back tomorrow with a contact and hook up the 2nd element.
Very frustrating and scary.
I would like a new furnace, one that didn't have sparks flying out of it, which could shorten it's life or damage the furnace. And a new blower, one that wasn't running nonstop for 6 hours, what a break in cycle!
Last but not least, when they removed the old furnace, there was a door. Now they took that and are not supplying us with a door. When I asked about a furnace door, he said "put a sheet up". Not only is the unsafe and a fire hazard, but ugly and unprofessional. I need a door so kids don't get hurt or my cat doesn't jump up and get hurt.
I paid all that money and you took and used my warranty AND I don't have a cover/door.
thank you guys for your videos they are very helpful really appreciate it god bless you all
Well that isn't what I would consider a homeowner fix, probably a stuck sequence without actually seeing the unit. Just shut it off and call an HVAC company to come work on it, pretty quick fix usually. If your LUCKY and your air handler has 2 breakers on it you might be able to shut one of them off that doesn't control the blower and see if the heat strip was on the one you turned off. Save some cash till the hvac guy can get there. It's a 50/50 shot which breaker it's on though :(
@brotherb30 ...no the thermal safeties can be replaced individually. Of course as long ad the safety is functional the contact surfaces could just be lightly sanded to clean them up. The tech just has to make sure that the connections are all tight. :)
Thanks for this video! I stumbled across it, and it's the same heat kit I have in my old Goodman furnace. I was happy to learn more about how it all works. :-)
Thanks man, you provide some really good information, I'm a new tech and I pretty much feel confident with everything, the only thing that stumps me are electric heat setups, especially electric heat setups that are heat pump systems, those damn DC relays have really made me feel stupid, if you culd do a video on how to replace them with sequencer, or just how to wire up a sequencer from scratch for a 2 strip or 3 strip system that would be most appreciated bro. Thanks
Mikie this is a really good vid. You helped me out in so many different ways. The only problem I am having now is finding out what sequencer is the right one. I had a guy come out last year and he said he changed the voltage regulator. He handed me the old part and from what I remember It doesn't look nothing like the one that's on it now. Well long story short, he died in a motor cycle wreck. So now I have no idea what part to buy. The one on it, is burning the ends off and timing is off. HELP
Thanks that really helped. got it back working now.
Impressive video Mike, where I live up in Canada we typically don't use electic heat, we have gas fired RTU's or hydronic heat. Maybe the occasional heat pump.
But it's good to know how these work.
You probably don't live in Quebec.
I had two thermal safety switches break, causing two heating elements to not turn on. I knew something was wrong because the house wouldn't warm up properly. Ordered new thermals and replaced them.
Then a relay contact that controls a heating element got stuck in closed position. There was no way to know something was wrong until summer came and the AC wasn't cooling properly. Also the electric bill usage seemed high for months. The thermals kept the unit from overheating. Replaced the relay.
Hey John!
Wow, that seriously sucked!! I've been on a few calls where the heat relays were stuck closed too. Go out on a summer cooling call because the house won't cool down, nothing looks wrong with the unit, coils are clean and filter is clean, but the temp split sucks and when I hooked my gauges up, the suction and head pressure were both high!
Got my meter out and put the amp clamp on each heat strip circuit and sure enough, pulling 20A on the double stack sequencer that had one strip on it and the blower motor on the other half. The blower part worked fine though.
If the house reached temp at night and the unit shut off, the strip still stayed on, overheated, and the thermal limit switch would shut it off till it cooled down, then it would heat up again, over and over. Yeesh their electric bill!!
I got lucky on the very first one that I found like that. For some reason, can't recall, I had popped the cover off the evap coil and could feel the heat radiating from the heat section!
Usually with those symptoms, high pressures, low cooling temp split, I assume that there is a return air duct that is off and its sucking hot attic air into the unit. I've run across two new installs like that, system was changed our during the winter so it doesn't get caught till summer!
Good work and catch on your system!!
Mike :)
I would find one these heating boxes like this one out of a furnace or duct heater and disconnect the unwanted elements. Don't know what the proper temp is for powder coating but I would make sure their is a thermostat to control temp. BTW I hear a old electric oven works well for powder coating has everything already set up. Just limited on size, fine for small engine parts. Unless you can pick up a commercial one.
had string break and layed against rack so it was getting 120 volts all the time but wasnt getting hot enuff to trip limits, baffled me for a second
@brotherb30 The heat strip is probably fine. Burned off wiring is typically due to a loose connection or loose terminal and that causes a higher amperage at that weak point to do the job. It heats up and melts off, etc. usually replacing the wire and making sure you have good connections. ...You would be surprised at how many calls I would get on a regular basis in the winter for just that :)
Are these supposed to glow red hot like a toaster, or do they give off a faint red glow ? I assume also that the all the coils are supposed to light up at once. I drilled a small inspection hole in my lower plenum, and used a cheap boroscope to view. I'm about to put a new heat kit in anyway, but i just wondered how bright these glow.
It varies on the coil string setup, but typically there will be some sections that will turn red (not brightly with the blower running) and others that won't. If the blower wasn't on to dissipate the heat then you would see more, until the thermal limit switch cut the power for safety. It's normal for them to work that way, the coil string give more surface area to create resistive heat.
As long as you have current flow going through the string then it's working fine. If memory serves a typical 5kw string will pull 20 amps, if you have a clamp-on amp meter it's easy to check and see if it's in that ballpark.
Heat strips usually last a really long time and usually only fail early if there is crying that builds up on them creating hot spots weakening the metal or rust from a water issue (dirty coil above it dripping or other water issues during the summer).
Hope this helps!
I took out the electric heat killed from a tempstar ac/heater and the heat coil isn't red all around when it heats, but only at the bottom and maybe 3/4 of up of a heat coil. Is this normal? Is the coil supposed to be all red when it's heated up? I turned up the heat to 85 degrees F and still the same thing.
Thanks a lot and God bless you
Thank you for your knowledge on furnaces. Mine had stopped heating. I watched several of your videos to understand what I see in my furnace, or more important is what I should see. 15 kw. I had a burnt wire and wires not connected. one of the elements was not hooked up. Connection from 60 amp cutoff switch went to both sequencers. power to two element coils ,but returned to the 60 and the 30 amp switch. I checked and I triple checked continuity and volts across the switches and elements. there was no schematic in the unit. I can't read the make or model number. The manufacturer is not even on the outside of housing. I have unit running once more all three elements work. It cycles properly. Cost : a trip to town 16 miles, 10 feet of wire and a package of wire connectors.
Sounds great, good job! The main failures I see on electric units are undersized wire that either overheats and burns off or does enough heat/cool cycles that it loosens the connector. And then melts or corrodes and burns. Then connectors that arent crimped well, they corrode and burn off or just melt off.
excellent video
What would cause the coil to have Several dead spots We replaced the coil with a new coil from supply house and had same problem
If you're talking about a single, say, 5kw string, as long as it has continuity from end to end (no cracks or breaks), you have power to it and it beats up, then it's working.
I've seen lots of heat strings that only turn visibly red in certain areas. As long as they're getting 240v (or whatever the equipment is rated for), all the connecting from the breaker box to the unit connections are tight and the house wiring from the breaker box to the unit is sized properly then its fine .
You can put an Amp clamp meter on one end of the string, if it's a 5kw string then it should be pulling about 20 amps.
That's what I've always done, unless it's a vertical unit and there was a water leak issue with the condenser coil for a long time (think really dirty coil dropping) and I need to check the coils for rust, then I would visually check them.
Hope this makes sense and helps!
I have that setup in my APT those are the most expensive way to heat. They really suck the juice
Mikie2501, I had a tech come out & it cost $200. $70. was to just come out & $125. for part (run capacitor) & labor of my HVAC unit & somewhat inspection & insight to another the unit has. It had NO Freon, needed 7.5 lbs & it's a GOODMAN unit. Now, someone came out & on the low side put in 7.5 lbs of Freon for $300. (different Tech). When the 1st tech checked everything he told me & showed me in the attic the capacitor & said it's just starts up the blower, I could even start it by hand if wanted & leave it on for air circulation. But, I said NO. We went back down stairs & tried it on heat & air NOTHING. Went outside to the unit, compressor line hook ups, NO FREON. Now, Freon $480. he wanted to fill it up plus the $200. I already was paying him. I said NO, due to money. I am a disabled vet, so you know the money fixed income deal. So he then showed how to put on emergency heat & that works. Then, borrowed some portable heaters from friends & used it with emergency heat, it's so-so. Tech #2 a friend came by, 2 weeks later put in 7.5 lbs of FREON, on the low side, outside but the fan did not come on?! So, in other videos the fan comes on or is on when putting in the Freon. Now, we have NOTHING? Lost emergency heat NO heat No air? The unit is almost 8 years old. I like the unit but from day one I notice it ran longer & longer each year even added window AC unit. What do you think is up with this problem?? When I call other tech or companies they don't want to hear it. They say set up appt. for them to come out $79. - $109. & inspect & fix ($$?) unit? Do you have any advice or comments for me on this problem for me? Thanks, PAUL in North GA. 1/19/14.
good vid. dam that take a lot of power.
Great job. I share your opinion regarding sequencers.
Goodman electric furnace 10kw MBR1200AA-1
Goodman HKR-10c
Costello heating and cooling installed a new furnace. They installed a Goodman mbr1200aa-1 ac, or tried to install. Very disappointed and frustrated. The owner, Gene, gave us a estimate. Then the next day had 2 young guys install the furnace. They did not know what they were doing. The job was supposed to take less than two hours. They worked from 9am to 2pm with the job not completed.
After they got "done" wiring the furnace, they flipped the Goodman breaker then flipped the main breaker.... sparked started flying, lit up the house! They wired it wrong and screwed up my new furnace.
The owner went to go get a circuit board and came back around 6pm. During that time, the Goodman was left running, blower did not shut off and the furnace heat did not shut off either. So for hours the thermostat was set at 63 degrees Fahrenheit and the temperature in the house kept raising up to 88 degrees. Unbearable and the breaker was too hot to touch to shut it off.
The owner arrived around 6pm to fix everything, the circuit board part, then realized he needs another part, a relay. Left to go get the relay, and came back around 8pm.
He got the furnace up and running on 1 element. So it didn't blow hot air, and it's 19 degrees outside! He said he would come back tomorrow with a contact and hook up the 2nd element.
Very frustrating and scary.
I would like a new furnace, one that didn't have sparks flying out of it, which could shorten it's life or damage the furnace. And a new blower, one that wasn't running nonstop for 6 hours, what a break in cycle!
Last but not least, when they removed the old furnace, there was a door. Now they took that and are not supplying us with a door. When I asked about a furnace door, he said "put a sheet up". Not only is the unsafe and a fire hazard, but ugly and unprofessional. I need a door so kids don't get hurt or my cat doesn't jump up and get hurt.
I paid all that money and you took and used my warranty AND I don't have a cover/door.
Thank you very much mr .jones
i pretty munch like gas or oil heat for central heat i use gas so the only electric is the heater that i use if i just going to heat one room at night or for extra heat
and for cooking and hot water
Great Video,I wanna see more video about A/C unit.please!
Turned on heater for the first time this year and a strong odor is filling the air. Just when heater is on, however, no smell when a/c is on. Cleaned primary pan. It did have a little moldy water in it that we cleaned but still having smell when heater is on. Thought maybe a dead rodent but no smell is in attic. HELP! Not sure what to do next. Unit is 9 year old Goodman electric central unit. Other than this horrible smell everything seems to be fine with the system.
Hi! Well while Ive heard of that situation, Ive never actually run across it, or if I have its been so long that I dont recall ;) (which isnt saying much with my bad memory, hehe;).
A lot of times when you get a smell after a while the heat will cook off whatever it is that was obviously growing in there, it just needs to dry out. However if it keeps on hanging in there and just doesnt seem to go away then you can have the coils (evaporator coils) treated. Im trying to remember if its an anti-fungal treatment or the like.
HOWEVER, depending on what kind of smell it is, it IS possible that you have a dead critter in there somewhere! Never fun! You might check, or have someone check, the ductwork in the attic, or under the house if its there, and see if you have had a rodent eat/tear through the ducts and get in there and die. (Lovely thought, eh?;). Ive seen mice/rats chew through, racoons are the worst if they can get a way in the attic! ...and the occasional squirrel too.
If the ducts are under the house and they are damaged then you could have water laying in them as well.
Sorry if this answer is delayed, Ive been slack checking my mail the last few weeks. Was the drainline clogged or any other obvious issues?
Hello. Where would I start if heat pump comes on but blower doesn't? The fan blower spins freely thinking its OK but when I manually turn fan on, all I get is a loud buzzing from handler. I don't have an amp gauge but I do have a volt meter that's rated for 10 amps. Can I use my voltmeter to troubleshoot this problem? My landlord refuses to call a professional and all his pointless visits hasn't helped. Any help would be appreciated.
Your landlord is probably required by law to pay a hvac licensed person to do the repairs on it. It sounds like it could be a relay or possibly a capacitor. A buzzing is usually a relay issue though. Normally you could try heat since it usually runs at a slower speed and uses a different relay, but some heatpumps use a single speed for everything. I have another video talking about testing the blower motor by wiring it direct, bypassing the board to make sure its ok. Some units have the relay on the control board and some have the relay off by itself.
+mikie2501 Hey Mikie, I put a new capacitor on it and blower still wont come on. I still hear the buzzing. I removed the fan yesterday and tried cleaning it, but that didnt fix it and there is a tightness in the motor. So it's probably fried. thanks for your response..
+brian Boggs ouch. Yeah, if the blower doesnt spin smooth and freely then its toast. Usually you'll get a humming if the bearings are shot and it cant spin up. Not the cheapest fix, and worse, you usually need a special tool to get the blower wheel off the motor since they usually stick badly over time.
+mikie2501 Yeah, I noticed that blade is on tight, so I will let landlord know about it. I'd really like to go ahead and fix it, but I do have a wood stove so I been splitting wood in the last few weeks....lol..plus he's 70 years old..
+brian Boggs lol, gotcha! Slightly different circumstances! I was thinking apartments or the like. Well at least you have a fallback solution! Id love to have a pot belly stove :) (though with my crazy cats... Heh)
My problem is that I moved my unit from one house to another. Now the coil does not turn amber and only heats up for about 3 seconds and thats it, fan works, thermostat works. It did work at my other house but don't know what it can be that does not turn the coil amber and hot. Is it possible that the thermal protector got ruined? Unit only two years old and probably under warranty, but paper work mixed in boxes from moving.
Hi! Honestly, thats not a lot to work with, it could literally be a million things... Could have a coil that was brittle and broke in transit that is barely touching, wiring problems, loose connections, its a ling list! You don't live in Ft Worth do you? Hehe. ...anyway it looks like you will have to call a tech. Kind of unusual to pull a unit from the old house and put it in the new house! Call the installer back out and have them do it right! They should have tested everything after they hooked it up. You may get a surprise later qnd the ac doesnt work either!
can you tell me what the six wires in the 9 pin plug are for on the goodman/amana hkr20C. I gutted everything on my system. and started over with a heat kit. I also got a brand new transformer. I have to hook up the fan, 2 wire electronic thermostat and a switch.
How can i eliminate all but one heat strip? I have the blower motor (2amps) and want only one heat strip (20 amps) on the 30 amps power coming in. i have a tree sequencer with four heat strips. How do i eliminate two or which two do i disconnect and tape off?
i have a ? THOSE 3 LIMIT SWITCHES DO THEY HAVE TO MATCH MINE CAME WITH L-175 40 I HAVE 2 NEW ONES BUT THEY ARE L-160 20F AND A L-175 20F WILL IT WORK
Great video, thanks. I have an old furnace I was looking at and it doesn't have the heat sequencers. Is it possible it's done on the control board? It's a 20kW with two 60A breakers. 4 x 5kW
Hydronic! I'd be lost, lol :> I do have a friend (retired pilot) who did a homebrew AC job on his hanger by putting tubing in the concrete and pumping whatever chemical he used through a hacked refrigerator/freezer combo, lol. :>
Question. I measured the breaker, two hot wires come in 220V. There are many small wires connects to the breaker. I measure both side left and right. 0v. Measured left side with grounded chassis, it showed 110V. Measured right side with chassis, it showed 110V. But I measured both side of the breaker. It showed 0v. Why? Did you see the something of your broken 60A breaker?
Hi I have a heat pump its runs loud outside both its heating good, I just see have the heat strip to in the furnace ( I am new at the heat pump) and I disconnect the wall non digital thermostat for the heat strip and I don't know how to connect back what wires thanks
Its like only one coil is coming on too. All the vents are blowing out warm air all except the first vent. My power bill is out of the roof. The heat seems to never wanna shut off. It just runs for ever and buy the time it shuts off, 3 minutes later it seems to come back on....You seem to know your stuff and are real good at it....PLEASE HELP ME MAN
Thanks! the problem I am having is that the heat strips are staying energized all the time. When I power up the system and run the fan the heat stips are energized...
One thing that causes that is techs make a very common mistake of replacing the fan relay wired up backward.
But also thinking the sequencer can stick on. I'm not sure but I think systems either have a separate fan relay or alternately integrate them in the sequencers.
You are awesome!
Hey Mikie, thanks for your video, it was exactly what happened the black wire was burned so I replaced it and worked just fine,,,,now usually how much did I save myself if you don't mind me ask you? Thanks again. Sergio Diaz
What can happen if the limit does not pop?
Question. My filter hasn't changed for 2 years. Originally not heat. Now the fan is not blowing air. Do you think the heat strip is broken that cause the fan not running?
great info on this video doing great
Hi Mike, great video. I have more or less the same set up as you showed at my cabin and the unit is in the attic. When we turn it on it runs and heats with out issue for two or three days then it wont kick on but the fan just runs while trying to call for heat. Watching your video it seem like it may be the sequencers, does that sound right or is this another problem? Thanks, hope you are still answering questions
I sure appreciate it sir. My thermal safeties seem fine however they have got some black burn marks on them. Can those be replaced themselves or does the whole strip usually have to be replaced? I am grateful for your responses. Thanks for posting these very informative videos.
@tkarmakid Hrm, that sounds kind of hinky! Trying to picture the unit in my head. ...but a 5kw heat strip 'should' pull about 20 amps when in use. Those are the most common anyway... I actually think I have 7.5kw strips on mine but can't remember what they pull. Might cut the breaker and check continuity and to ground on each heat strip, check the wire sizing and make sure the goob installers wired the right breaker size to the right strip. Not 2 strips to a 20 and 1 to the 40 :)
According to Ohm's Law 5kw strips @ 240vac should be 20.83 amps and a resistance check should come in around 12 ohms.
Oh, funny, I just noticed it's an 8 yr old comment, lol. Well maybe someone will find it useful.
hey quick question if the heater comes on and runs till it meets temp but when trying to come on again the heat strips heat up but blower won't run could that be fan relay or sequencer? Thanks in advance
thank for the vidio
how would you t/shoot a heat pump connected to the system.?
The stranded wiring they use on those kits is different than standard household wire. I believe it is appliance wire. It seems to have different amp rating limits than regular house wire how they use it on the kits. I cant find any data on the amp limits of that wire on the internet. Do you have any idea about the limits of it?
Hi, I have an old electric fan heater which I had to take a part to fit it in a smaller case, unfortunately I messed up the wiring!! can anyone explain how to join/ connect the power, fan motor to the 2 heating wires please? thank you very much
Hey Mike, unit runs, but heat is low coming out of vent. extended run period also?
goodman air handler.
Are the thermal safeties, are the 24v and can they be replace with a general high limit switch as long as the temp is the same?
No, they are high voltage. Remember, they are inline with the heat strips! They do make adjustable ones that you can set the limit on, but I can't recall off the top of my head if they have them for high and low voltage. (Ele. Heat vs gas heat limits) I dont know why they wouldnt. Should be easy to search for though!
Does that heat strip give info on how close it can be installed to combustibles. Heat shield required if duct is too close to strip.
thank you
Hi Mikie, What gauge of wire is used to the 240v terminals of the sequencer were they tend to burn out? Is there a special terminal into which the wire is crimped to use that will handle the high voltage. Should it also be soldered to have a good connection. Thanks
Hi! Those are good questions! Most supply houses will sell crimp connectors that are rated for high heat. Typically 12 gauge stranded wire is rated for 20amps, I think some of the manufacturers use a higher strand count when they build it, but reg 12 ga will work fine.
Over time, hundreds or thousands of cycles,the connectors heat and cool, back and forth till they get weak and stretch, then corrosion can get into the connection and start building up, which means higher amps to push through the crud. It just gets worse and worse until the connector burns/melts off!
Something I run across a lot more than I should is going on a call for burned off wires only to realize its been repaired before, but instead of using 12 gauge, they used scrap wire from the back of the truck, which is usually 14-16 gauge bits left from a fan motor! It will work but at some point it will melt eventually because the smaller wiring cant easily handle the 20a.
My furnace has only the top heating elements working but the bottom are not. We move the top wires to the bottom and bottom to top and the other elements work but not all. Any ideas?
First, I can't emphasize how safe you need to be while working with that. I'm assuming you have all the breakers off and know how to test for live voltage with a meter, one mistake and 240 volts will kill you :(
Anyway, that said, if I understand you correctly you are saying you think all the elements actually are fine, just not getting power.
First I'd check every wire connection to make sure there aren't any burnt off wires.
If that's fine then it's most likely a sequencer, or relay, depending on which you have that activates the circuits.
You might have separate sequencers for each heat strip, or you could have two strips on a double stack sequencer and half the sequencer isn't working.
Of course this is assuming that something is actually wrong. Are you just inspecting the unit or notice a heating problem?
Sometimes a unit will be installed in a house but they don't actually need that much heat for the space and wiring up all the elements would be too much, so they leave one out of the loop by removing wiring in a spot. If that's the case then it might not even have the proper breakers or wire sizing to add in the extra heat strip safely.
mikie2501 this was working fine but then it wouldn’t heat up to temp. I replaced both sequencers but it still runs the same. Barely warm heat. Since the elements do work when moving the bottom wires to top and top to bottom, I’m not sure what else it could be. It is a Goodman hka-20c. I’m going to check everything and run some meter tests. It might be best just replace the kit.
mikie2501 I got it. One of the sequencer wires needed replaced. It is working again.
@@rwgpublishing929 awesome! Yeah, sometimes it's easy to miss something even though you've looked at it three times, hehehe!
Well you know what they say about a mechanic not working on his own car, I have this heat/blower relay that literally melted half off a number of years ago, I grabbed a bigger relay and just moved over the stuff that was burnt and piggy backed the low voltage to tun it, about time I get around to pulling out the old relay, hehe. I shoved in a big ole outdoor condenser contactor to do the job, thinking 'it won't overheat and wear THAT one out!!'
Two bits of fun, you can hear the very audible ClacK when the contactor closes, hehe, doesn't bother the wife though, so I'm safe! ;) ...second thing is more of a pain, at the start of every heating season when the heat *should* come on, nothing happens! Turns out the plastic slides the double pole contactor slides in tend to get stuck from just sitting and collecting humidity/dust all summer, so off the cover comes, then two cover plates that are the most assinine setup Ive ever seen, forget to turn off the main breakers as well as the service disconnect and make one slip with that plate cover and you hump the mains wiring before it gets to the disconnect!! :/
Anyway, get them off, power it up and call for heat, then take a screwdriver and give the contactor a good wack with the handle end and it snaps closed! Mmm, the smell of burnt dust on the elements! Always gets the cats looking around, hehe! Cycle it two more times to make sure it works, then kill the power and put the covers back on. Done! Pro tip: never put things back together till you test it, Murphy will get you every time! Hehe!
So, was it a burned off wire or had the connector end softened and come loose?
I used to get calls every year where I was replacing burned/melted wiring on heat strips on older units. At some point someone had replaced the wiring and they put undersized wires in that invariably overheat.
Makes me remember this older couple in this huge, old two story house... Called me out on a home warranty insurance call, saying something was wrong with the unit because the winter bills were always so much higher than the summer.
I go up into this walk in attic (gawd I love those!!) And here's this antique as hell air handler. Open it up and its so old it uses contactors Ive never even seen before! Then I start checking it out, the thing used 35kw of heat!!! Holy. Crap. Thats about 140 amps at 240v. Insane!
mikie2501 what jobs you have. I have ran into so many crazy things but with the tester, sequencers that I replaced it was a $50 fix. Since it was only a wire, now I have two spare sequencers. Lol
how do u rewire a relay for a heating and cooling fan fro a Intertherm gas furnace
What is the reading suppost to be on a limit switch when is bad??
A limit switch, like a sequencer, can fail in either the open or closed position. If you had one laying on the table and put your meter on it, the resistance would be negligible, basically acting like a straight wire.
If, however, it showed as an open circuit (say, testing in the continuity setting) then it's bad. The limit switch is just like an on/off light switch, when the furnace gets too hot the little concave disc in the switch pops the other direction and opens the circuit, cutting off the (usually) 24v going to the heat strips sequencer or gas valve.
I've seen them wired a lot of ways, but typically, properly, they should cut the heat call while leaving the blower running until the temp drops lot enough for the disc to pop back to normal, then it will let the heat call continue, or wait for the thermostat to tell it to hear, if the temp went up high enough in the house while the unit was cooling down.
Usually the only time I've found one failed is it there is either an air flow restriction that is letting the unit overheat again and again, short of short cycling repeatedly before the thermostat reaches the setpoint, the repeated excessive heat wearing it out prematurely.
Typically an airflow restriction would be something like a really dirty evaporator coil, or a clogged up air filter. I've seen insulation board in either the plenum attached to furnace/air handler, come unglued and fall down inside the unit or plenum blocking/restricting airflow. A few times I've seen (like two times ever) the blower wheel locknut not be tight and the wheel would be spinning in the motor shaft. (Fun figuring that out the first time, haha!)
I once or twice I've gone on a call and at some time in the past three blower motor had been changed out and the blower had been set too low a speed, say set too low when maybe it should have been medium low or medium. ,(Some replacement motors have the or four speed, high almost always for cooling.
The only way to test the limit switch is to overheat it. The temp is usually marked on the limit switch. Either removing it from the circuit after shutting off all the heat breakers. (On electric heat air handlers there are almost ALWAYS two or more 240v (in the US) breakers!! A really small unit might have one)
Once it's out of the circuit you can get some alligator clip jumper wired and use those to attach your meter leads to the switch, set it to the continuity/been setting. It should be being out showing continuity. As you heat up the business side of the switch and it reaches temp it will open the circuit. Then go get a glass of tea while it cols of so you can touch it again to put it back in the unit ;)
The other way would be, set the thermostat to heat and turn it up high so it will lick on when you need it, then turn off the breakers to the unit and then remove the 24v wire going to the blower relay securing it so it doesn't short on anything, then turn the breakers back on. The gas furnace should fire up, or in the case of an electric heat air handler you need a meter with an amp clamp that you can clamp over one of the incoming 240v lines, set to high, say 100A or higher.
With gas you just wait for it to hear up the heat exchanger enough to trip the limit switch, with electric you watch the meter to see when the 20a or 40a or whatever it is drops down to almost nothing, then you know it has cut the 24v signal calling for heat.
I don't recommend doing either of these under normal circumstances though, it puts extra heat stress on the heat exchanger or electric heat strips, not worth the trouble.
So the short answer (hah!;) Is, if it's not broke, don't fix it. If it is and the unit is cool because the heat won't come on any more and you find the switch stuck open, replace it. :)
Just for fun, here's the order from most common heat failures to the least, on electric heat air handlers:
1. Heat sequencers.
2. Burned off wired, usually with corrosion, from the push on connectors being too loose. On older units that have had a lot of repairs over the years I've sometimes found some tech had replaced burned wired but put on new wiring that wasn't heavy enough gauge, as was originally there.
3. Blower motor failure.
4. Blower motor capacitor failure.
5. Control board failure. (Nearby lightning gets them sometimes) there are too many ways it can fail to get into here, but not all units actually use boards, lots of old ones out there that don't.
6. Bad 24v transformer. Lots of ways to die, usually from a dead short in the low voltage wiring and there was no fuse inline to save the transformer!
It always kills me when the manufacturer is to cheap to include a part they can get in bulk for pennies, lol!! Lightning can be a culprit too, but usually other stuff in the house will have been fried too, heh.
7. Failed/ bad heatstrip. This is almost always on old units or systems that have leaked water on the strips during the cooling season and rust/corrosion had set in until it gets a hotspot and fails, or unfiltered air let's cut build up on them slowly over yesterday causing heat stress, then they break.
8. Blower wheel failure. Very rare. The central disk breaks loose from the shaft nut attached to the motor and doesn't spin properly with the motor, which can cause motor failure if, say, it goes unnoticed when nobody is home and the unit keeps running.
9. Limit switch failure, reasons listed above.
I've left off a few, such as bad contactors (some brands use them instead of sequencers) either for the heat strips or the blower motor.
Bad thermostat, dead, not working properly out a new one was installed and not set up properly. (I've been on a lot of calls for that)
On gas furnace there's also bad thermocouples (won't stay lit),
bad gas valves (not coming on even though they are getting a call voltage)
Clogged pressure switch nipple. Where the mounted pressure switch has a rubber tube that pushes onto a nipple going into the induced draft motor. Rust that gets sucked into the nipple blocks up the tube and has to be c cleared, but that also points to a bigger investigation looking for the cause of the rust.
Pressure switch failures. (I hate those!)
Hot surface element failures. These ignite the gas on modern units. Do lots of these every year!
Flame sensor failure. Usually due to soot building on the steel rod, clean it with some sand paper, wipe and reinstall. Occasionally there's a grounding issue with them, but that's less frequent unless it's a package unit outside.
Well that's it!! Hell, I should print this and make a video covering it all! Hahaha!! Hope you found this entertainment, if nothing else!
Mike
So my air handler heater coils are running ALL THE TIME regardless of whether I set it to cool or hot. The top ductwork above it are too hot to touch if I leave the breaker on. There doesn't seem to be any thermal protection working at all because the heat apparently has been runing like this for MONTHS and cost me $100+ extra a month on my bill. I have the panel popped off and see the two heat sequencers you show in your video. I hear a buzzing sound coming from the aux heaters as if they are running when I turn the breaker on and when I set my thermostat to COOL mode the aux heat still runs/buzzes. The top vent gets hot to the touch after a few mins so I know its on. Should i replace the two heat sequencers? Anything else I should check?
Well it definitely sounds like a heat sequencer. The only other thing to check would be to check the low voltage coils on the sequencers to make sure it isnt getting power telling it to switch on. If you're not used to working with high voltage then I would not recommend trying to check it, its way too easy to accidentally touch the high voltage line and short it to the low voltage side, causing all kinds of problems! Not sure what your buzzing noise is unless you have a noisy transformer or something. The limit switch is probably working, the problem is that it prolly cuts out at like 130 deg or something, but as soon as the unit cools off below the cut in temp, it just turns it back on until it overheats and trips again. (When the blower is off)
Let me know what you find!
Good videos
Thanks for the video. What may cause the heat strips in a heatpump to not come on during defrost cycle?
Hmm.... Thats one of those ones where you want to see it to figure it out, hehe. Well initially I would think something is wrong with the defrost control board. Of course it could be something as simple as it was never wired up when it was installed too. The sequencer or relay that its wired to could be bad. If you arent actually checking it with a meter it still might be working, you often wont get any warm air coming out, just less cold, heh. You have to remember that in defrost mode its the heatstrip fighting against the cooling cycle so you get lukewarm, if that, at best. Depending on the age of the system the heatstrip(s) could be bad too.
The heatstrips are easily tested by running it in emergency heat or auxiliary heat mode (depending on how your thermostat os labeled). Its also worth noting that they dont always turn on all the heatstrips in defrost mode, just depends on how it was wired. Having issues with it?
Very helpful...i'm doing some troubleshooting on my electric furnace at the moment. everything seems to work its just that the coils don't seem to be heating up like they should. the air that is being blown is only luke warm. I did the tests that you showed in the video and all seemed fine. One question i had was that when i test, with my unit running, across the sequencer. assuming that it should be closed, what should the volts read? no volts is good and means a closed circuit? I have 3 sequencers and one of them was reading 240 volts while the unit was running
Thats probably why your air only feels luke warm! :). You have two heat strips firing and the third isn't. Most likely you either have a bad heat heat strip or the sequencer is bad. Usually its the sequencer. Next time you are testing the system you can test that strip and the sequencer.
Start by cutting all the breakers to the unit. Make SURE to test ALL of the incoming power lines to make sure you got it all shut off. There should be at least two breakers on a three strip unit, probably a 60 and a 30 amp breaker, assuming they are all 5kw heat strips.
When you're sure its dead get a flat-blade screwdriver and a pair of pliers. I usually push the screwdriver against the metal tab where its riveted to the sequencer and then use pliers (or fingers if its not too tight) and pull the wire off. If you just pull the wite sometimes it will break the sequencer. Its easier usually to pull the wire off on the heat strip ceramic though unless its a tight spot.
...anyway after you have the wire off so that the strip isnt electrically connected to the sequencer then you can set your meter to continuity to test the heatstrip... If you touch your leads on the meter together it should beep, then you know you have it in the right setting. Put a lead on each end of the heat kit and if the coil is intact it should beep proving the circuit. (thats why you have to disconnect one side or it will read backwards through the system)
You can also test the sequencer. Easiest way is to go ahead and completely remove that wire from the furnace so its not flopping around. Power the system back up and call for heat. After the other two strips fire up wait a bit to give it enough time to come on then check the coil side of the sequencer to see if youre getting 24-28 volts. Be CAREFUL not to let the meter lead accidentally touch the 240v terminal above at the same time or you'll fry things!! If you get voltage and you know the heatstrip is good then the sequencer is bad because its not closing the circuit.
Sometimes you can gently smack the top of the sequencer with a nonconductive tool (say the butt end of a rubber handled screwdriver) and it will unstick. ...but if it got stuck once it will again, and you run the risk of it sticking ON as well! Lol.
I went on a call in the summer once, lady said the unit wasnt cooling, pulled my hair out till I realized what was going on, her freon pressures were high on the low and high side, but her coils were really clean outside so I went inside to see if the return duct had fallen off and it was sucking attic air. That was fine but as I checked further I realized a sequencer with TWO heat strips on it was stuck on! It was heating and cooling at the same time! No telling how long it had been stuck! Wouldnt want to see her electric bill, lol!
Anyway, this is really something you should get a technician to work on since your dealing with 240 volt stuff and a slip could electrocute you! (My standard warning!). The sequencer, if that is bad, usually has a set of numbers on them denoting when they come on and go off, like 1-30 on 60-90 off or the like,on the sequencer or the plate, this is so the sequencers step on and off in the right order. Sometimes the blower motor is wired to one of the sequencers too, so its important to replace a sequencer with one that is timed right!
Hope this info helps, time to call a tech though, you dont want to run it very long with just two strips, this will run your bill up because it takes way longer to heat the house! Been there, done that! Take care!
COMO
Will throwing the breaker for 15-minutes or so reset the sequencer?
Hi Mikie, like your HVAC and Ham videos. My next door neighbor had an electrical fire from the sequencer in they're furnace yesterday. Its been in the higher 70's here in northern Ohio. They wouldn't have turned the heat on. M1 to M2 was burnt to a crisp. M3 to M6 was fine. Some of the wiring insulation was burnt. Isn't the sequencer only for a call for heat?
when installing an element in an AC unit do you need to have a delay switch to let the element heat up before the fan turns on?
No. The blower motor always comes on at the same time as the first heat strip. You might have a delay for the other heat strips coming on and going off, or not depending on the unit. When the house reaches temp snd the tstat tells it to shut off, the system will either shut off everything at the same time, or it will cut off the heat strips first then let the blower run for a bit longer to get the rest of the heat in the house and cool the unit. Hope this helps!
Lol! Broken and touching ground so just half a leg? hehe nice!
Great video. I'm setting up a portable job heater with a hka-15ca heat strip like the video. Question is can I run one 4 guage wire bundle to the 50amp, and jumper to my 25amp supply disconnect? Or do I have to run a separate like 10 gauge wire bundle to the 25 amp disconnect? Thanks
It may be a bit large for your needs but I just plug in an electric clothes dryer on a dolly cart. I made up a short heavy extension cord to the 30 amp dryer plug. Takes the chill off pretty quick in vacant houses in the Pacific Northwest.
The white wire is the 24v call for heat from thermostat? Right? So is the blue wire the 24v common on the heat sequencer? So I should read 24v when I put leads on each 24v side of the heat sequencer when heat is being called for? thnx!
One side is hot, the side you are controlling from the thermostat, and the other side is common or neutral if you prefer, singly or tied to the other sequencers. It doesnt matter which side you hook up to on the coil. When you call for heat from the thermostat you should read 24-28v across the coil from one wire terminal to the other. Just be careful not to accidentally touch the high voltage terminal above at the same time or you'll fry the coil :)
Ok perfect. Thanks man! Good videos!
I'm
If it was a short it would trip the breaker right off the bat. When you say it shuts off, do you mean it trips a breaker or that the heat strips shut off but the blower continues to run? You should have a contractor look at it. It could be anything from improperly sized wiring from the main breaker to a very dirty evaporator coil opening up the temp safety. (depending on what is shutting off) Not overly helpful here, sorry, you need to have it looked at! :)
My heat pump blows cold air inside so long that we get cold. Is this normal? Please someone help me know if this is normal for my Amana unit
Would really need a better description of what is going on with the unit to make any guesses. Heat pumps are kind of hard to troubleshoot verbally anyway. Is it heating mormally then starts doing it, only puts out cold air? Is it actually a heat pump, meaning it uses the outside unit during winter? (some people just say heat pump even though they mean any kind of heat they don't know exactly what they are trying to describe.). Try and give me a sequence of events. Does it sometimes work right? What is the outside temp when its blowing cold?
Hey Mikie, I test the high limit thermostat and it was good. The unit is blowing but no heat is coming out. I only have one set of coils. How do I troubleshoot that?
What is the KW on your strip kit? If 5kw, that aprox 17k btu/hr. Will not be very warm. 1 KW = aprox. 3,400 btu/hr APROX.
Hello .Thank you for yours videos. Is the coil heat strip bad if only parts of the strip glow when it's heated? Thank you
No. If it glows anywhere, it should be working. Those red areas are simply not getting cooled as well as the rest.
Hi Mr I know this video is old. But it has very important information. I will be very thankful if you can give me the model number of or part number from those. Brakers or service disconnect.
I can't find it anywhere.,for my electric heater. Thank
So these e furnaces run on 2 wire 240? No neutral?
Thanks very useful .
Hello Mikie, good video man... I got to remove an old wiring from some really old systems at a apartment complex, they have heat strips 5kw.. im having a little problem tinking how im gonna rewire that with the new components, by any chance, would you have a diagram or something showing how to propper do so?.... thanks man!!
Great can u show me how to troubleshoot walk in coolers and freezers
Man Great Video. Showed me all I need to know. I keep getting a burnt wire on my thermal safeties. Any "typical" cause for this? Could whole heat strip be bad? Any help would be greatly appreciated.
Thanks Mike
I have furnace it don't do nothing what do I check
So is the purpose of the sequencer to give the fan enough time run up and or sequence the start up load ?????
Thank you.
Spreads out electrical load between multiple heat strips.
thks mikie this was helpful
If you're reading constant voltage through the sequencers then chances are the sequencer is bad?
Trying to see if I understand your question... If I have a sequencer that had 24v applied to its coil, activating it, and Ive waited the proper amount of time for its contacts to close, then if I put a meter across the High Voltage terminals on the sequencer and show voltage then it is bad. If I do not show any voltage then it is good.
When electricity flows from one terminal through the closed contact and out of the second terminal, then the voltage that the meter sees at both points is the same voltage so it doesn't register. If, however, it is broken and fails to close then your meter will read a potential voltage across the contacts on the meter.
Dont forget to verify that the coil is actually getting at least 24volts (if thats what its using, some are 120v coild), if its not getting voltage you have another problem to fix too! Mike
How do o replace my round ceramic insulators
At 4:17 in the video, you suggest that 240v is carried thru the wire and to one side of the coil. Is the voltage coming in that side 240v or 120v?
+Melvin292 it's effectively 120v to each side, but the load gets 240. Think of it like plugging in a three prong welder or dryer, you have the ground and two 120v legs to give the work load 240.
Heater unit in my condominium has 3 coils the same one as its in your video. The top coil#1 got cutoff but the blower runs so I replaced the coil. I don't see coil#2 heating up, it looks in good shape and multimeter shows continuity not sure why it doesn't work. Coil #3 gets heated up correctly as soon as the blower starts. I had a backup 2.5KW coil so I replace coil#1 with 2.5KW instead of 5KW, will this a problem? Any idea what must be wrong with coil#2 or will it heat up after the other two are heated correctly. I didn't notice coil#2 heating up for first 5 minutes. The system runs for more than an hour and suddenly 50AMPS Circuit Breaker(CB) tripped OFF. I switched it ON and unit started again. Any idea what must be trimming the 50AMP CB?
+snehalshankar wow, sounds like you have a few issues!
First the replacement coil; it wont cause any electrical problems, but the system will have to run longer to do the same job, which could cost more money.
Coil number 2. If the coil is intact then it could be a few things... First check the wiring to see if it is even hooked up to run. Sometimes they will install a unit with, say three heat strips, but the house/apartment isn't that big and doing the math says just to use 2 heat strips, so they will disconnect one.
If that's not the case then next carefully inspect the high voltage wires going from the heat strip to the limit switch and then to the heat sequencer to see if any corrosion has caused a wire to burn off.
If that all looks OK then its a matter of whether the heat sequencer is bad or the sequencer isn't being told to come on. ...assuming that the sequencer is good, look at the low voltage wires that activate that sequencer and see if they are a different set than what is going to the other sequencer(s).
Does that heat strip have a sequencer all to itself or is it a dual sequencer and it has another heat strip on it?
If the wiring looks different then that strip might be set up as emergency heat. Do you have a heat pump system or a dual fuel such as gas/electric?
Regardless if the other stuff looked fine then its probably time to start checking a few things with the meter. Let the system run about 5-10 minutes then check the voltage ACROSS that heat strip. Check it on both sides of the limit switch to see if that is the problem too. Then if you still aren't getting power you can check to see if you are getting 24v too the sequencer coil to turn on the sequencer.
The 50A breaker. Speaking of breakers, did you check to see if you are getting 240v from the breaker box for that sequencer?
With three 5kw heat strips you should have two breakers. Two strips on one coming to about 40A and usually the other will carry the extra heat strip and the blower motor and transformer.
If they only wired two heat strips they might have shoved the blower and transformer on the 50A breaker along with the two strips.
Cut the breaker off and check all the wiring lugs for it in the breaker box and the disconnect at the unit. If they are loose then the breaker will overheat and trip. It gets weaker over time when it trips and you have to reset it.
If they are tight then check the blower motor capacitor to see if it is weak or going bad, causing the blower to pull more power.
..remember this is all high voltage and can kill you! Always best to hire a tech to work on it.
Well that should be enough to get you started, lol :) I'm typing one fingered on my tablet with about three hours sleep for the last few days, so I might have forgotten something, hehe!
I'll look forward to more system info and an update!
Mike.
Thanks for such a detail reply. I found the issue and it was thermal link open on coil 2 which I changed so was easy one. The tripping of CB was happening due to wires going to sequencer from CB was getting too hot at sequencer terminals due to corrosion. I cleaned the corrosion with slight scratching with screwdriver and plugged wire back in and after that CB tripping off has stopped also I changed filter so not sure which one helped but good till Yesterday. I also replaced coil 1 with 5kW and everything worked like charm till yesterday. Due to very low temp outside heater wasn't heating the house when I opened I saw that coil 1 5kw thermal link got open so I replaced and made it back to normal and worked with proper heating in house. This morning again the heater stopped heating house and blower is just running so I think the thermal link might have got open again. I am not sure what is causing it to blow. Any suggestions will help. Should I change other two heating coils to with new, is that causing load on coil1 and blowing thermal link fuse?
+snehalshankar man, UA-cam drives me freaking NUTS with their messaging! They make me hunt all over trying to find where they stick them, argh!
....anyway hmmmm.... Im assuming #1 is the last in line, meaning that the heat from the other two is blowing across it?
Lets stick with looking at it from an airflow issue. Have you been able to inspect the evaporator coil and see if it is impacted with dirt and crud? (The side the air blow into, obviously) that could slow down airflow enough to push the temp up too high on the thermal link.
Check the attic space to make sure that none of the ductwork has been crushed by anything up there, blocking airflow.
Depending on how its installed, pull out the air filter and get a flashlight and see if an old, dirty filter got sucked into the system. (May not apply for your setup. My brother moved into a used house and called me. The unit was in a closet. It appeared to have no filter in it but i pulled the case cover to inspect the evap coil, there sat a NASTY looking filter, twisted and pulled in. The evap coil was nasty too! It cooled, not very well, im surprised it wasnt freezing over! Had he tried heat it would have been opening the thermal limits constantly!)
Say, you talked about the thermal links, but does it also have thermal limits that reset?
+mikie2501 Thanks a ton for your answer. I have to check about he thermal limits if it gets reset. When should it get reset? I just see in when the heater starts it first load that coil start heating one by one in order as 1st blower starts, 2nd Coil1 which is at top, 3rd coil2 and 4th coil3 and they all keep on heating till the thermostat triggers it to off/stop and later the blower is stopped. I just see that coil1 for which the thermal link got open heats more than other two so not sure if it has to take with thermal limits.
+mikie2501 Thanks Mikie here are my updates::I re-stringed the other two coils because they were not heating bright and now all my three coils 5kw each are brand new which came with 250V 15A TF 152Deg C thermal fuse link connected one via thermal limit. At very first time when heater started it tripped off the 50Amps circuits breaker in 10 minutes of working and stopped blower(complete heater was shutdown). After switching it ON for another 15 minutes it tripped off again. Later I switched it on again and then it didn't break and it worked till date. Suddenly this morning due to freaking cold heater was running for a long time so coil#1 has stopped heating due to thermal fuse link getting open. I checked the current and it shows 19Amps so not sure that cause the fuse to open. I am not sure if this unit which is 53000BTU needs to have fuse link for 5kw element or can be directly connected to thermal limit(I read somewhere that thermal limit will open in case of high temp and then reset back ones cool down). So far I have changed 3 thermal fuse links with same specs( 250V 15A TF 152Deg C) for coils#1. The thermal fuse link came along with the 5KW heating element. Do you have any suggestions for the failure of CB as well the thermal link. What is the general specs for 5KW thermal link? I am thinking the one I have is not working for the unit I have so want to try changing. Thanks in advance!!