Mercedes Aux Fans, Engine Cooling & Air Conditioning Explained, Coolant Sensor Tricks R129, W124 90s
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- Опубліковано 29 чер 2024
- Described in detail what the auxiliary fans do, their importance to engine and air conditioning cooling, coolant temperature sensor modifications, stage 1 and stage 2, high and low speed fans. Video applicable to all early model R129 SL, including the 500SL, 300SL, 320) most W124s and helpful to the remaining R129s, 1980s and 1990s Mercedes-Benz
Auxiliary Fans serve multiple purposes and this video shows their what, why and how and includes the logical steps to help you diagnose any faults you may have.
Location of parts shown in the video will vary by model and year of car, but they are there.
Parts* referenced in the video:
R15 Resistor (000 158 3245)
B10/8 Coolant Temperature Sensor (008 542 4517). Blue Tip. Torque to 25nm
S32 Air Condition Pressure Switch (Green)
K9 Relay (001 542 8219)
* Always check for exact fitment with your year and model, when changing parts.
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Disclaimer - The content of this video is available for informational and educational purposes only. It is not intended to be a substitute for professional advice. I do my best to provide accurate and complete information, however, I assume no liability for any property or personal damage that may arise from any of the information contained in this video. Due to factors beyond the control of Handy Val, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Handy Val always recommends safe practices. - Навчання та стиль
As an R129 US spec SL320 owner, I really appreciate your videos. These things are brilliant references for years to come.
good informative video
Fantastic video, top work. Explanation is perfect
Thank you.
We greatly appreciate your knowledge about autos.
Thank you. More to come!
Your explanation and DIY videos are pure gold !!! Thanks thanks a lot for them. I will try to add a 1k Ohm resistor to the blue overheating protection sensor (B10/8) hoping it will result the Stage 2 - Fans at High Speed - come on at about 95degrees Celsius. Greetings from Hungary where the summers are freaking hot.
Thanks for watching and leaving such a wonderful comment about my videos. The 1k Ohm resistor will work and will get those fans operating much sooner. I have never travelled to Hungary but know a few Hungarians in Canada. Its summers sound like those in Canada - hot!
Very informative!! Thank you so much
Thank you. In this video, my goal was to take an important but confusing topic and try to make it more understandable.
Getting to know the resistance values of the "blue" ntc coolant sensor made my day. Thanks! I believe mine's faulty, because my fans are always working.
Since I work with refrigeration, I was able to test the high pressure switch S32, it should close when higher than around 20bar (old type, red sensor) I believe. So, I believe my blue ntc sensor is bad. I hope, since it's probably cheaper than a relay.
Glad it helped! The blue sensor is fairly cheap to replace and new ones are still available, whereas for the relays, new ones are much difficult to source but are available used.
@@HandyVal I tested mine a couple of hours ago, with the multimeter. It's "open", no resistance reading. So I'll have to replace it.
Is there any special procedure on bleeding a 200e engine? Or is it as simple as letting it idle and topping up the coolant?
Thanks once more, Your channel is very helpful!
@@Hellblazzer You got it right by idling it and topping it off. There's also a little bolt on the thermostat that can help you bleed the system. I made a video on changing the coolant reservoir, where I provide some other tips on bleeding and coolant in general - although it's specific to the R129 engine it's also helpful in your situation.
@@HandyVal thank you very much! I'll give it a look.
I changed the thermostat and sensor both aux fans ran, put the old sensor back in all ok with fans ,, I am currently chasing a high idle rpm it sits at 1500 rpm, sometimes it drops back to 700 but for now its decided to sit high, any ideas would be really kind and useful and gratefully received. I tested the replacement thermostat and it didn't open !
Best regards from high idle in Cheshire UK. where it rains a lot, no climate change here its always rains in the summer. I learnt a lot from you today and i am a very grateful Brit. I"m on a roll so will continue,
I brought the car as a 50th birthday present for me, i am now 72 going on 73, its a great car but i stored it for 7 years , so have been changing a lot of items to make it roadworthy , Each year, once a car goes over three years we have to have a government test, ( they also do this in Thailand) and they are called MOT that stands for ministry of transport. My SL will fail on a rear brake pipe that i cannot get to, the MOT garage has agreed to replace, apart from that the car is in pretty good shape,
I mentioned Thailand as that's where i retired to but am now back in the UK, My Thai wife does not want the car in Thailand possibly she thinks too many girls will want to jump in the front seat with me. She thinks the car is way too sexy and is a girl puller .
Today she mellowed and said yes we can take it, I signed the car over to her 3 years back and she has to own it for 5 years to avoid Thai import tax and VAT which is a bastard of a tax too. The problem in Thailand will be the BIG SPIDERS and nasty snakes may just make my SL their home , i went toe to toe with a King Cobra three years ago , managed to whack it. I got lucky with a long handled shovel.
In Thailand they drive on the left as we do so no probs there. The previous owner spent a great deal on the car as i have, and he also said it was the first one to be imported into the UK,
For my sins i also own a W212 E class and that is a backside of a Mercedes, the rear subframe rotted out and Mercs replaced free of charge, Comparing the build quality of my 1989 SL to my 2013 E class the SL wins hands down every time.
Anyway once again my thanks for this video and any news on a high rpm would be very welcome.
William - The R129s don't like to be stored for too long. Using them, even sparingly, is typically the best preventive maintenance advice to give. There are two main culprits for a high and erratic idle: 1) Idle Control Valve and 2) Vacuum leaks. A dirty or malfunctioning idle control valve will give you all the symptoms you shared. It can be cleaned or replaced, depending on your budget. Cleaning may not always work. During the car's storage, this part might have seized. For vacuum leaks you want to check all the little vacuum tube lines (many visible with the hood open and filter boxes removed) and their rubber tubes/connectors - you are looking for anything that may be disconnected, brittle/broken or rotten. Rubber and those tubes, with or without use do deteriorate over time.
Thanks for sharing your experience with the SL and Thailand! I agree with your view on the newer Mercedes - I too wonder how they'll hold up when then get to 30+ years of age. Keep us updated on the idle problem.
Thanks for the video Val ! My problem on the S320 W140 is the aux fans stays on even when the ignition is off. Maybe do you have an idea what causes this ?
Thanks for watching. Let’s diagnose this problem of yours. This is likely your engine harness. I believe your car has the biodegradable wiring harness and this could be one of many symptoms of a bad harness. Does your car have other problems? Do you know if your harness was ever replaced? It’s costly so let’s try some simple things first: for the items shown in the video, notably the blue sensor remove the connector, clean the contact pins and pinholes with a light sandpaper scuff and then a spray of contacted cleaner. You could also try replacing the blue sensor - they are cheap to buy.
I think in your version of 320 by removing the connector on the blue your aux fans come on, so it could be a bad blue sensor or a bad connection. Keep me updated.
Thanks for the quick response! I’ll keep you updated.
Very much appreciate your video Val. It is so helpful to know at least what components we are looking for! I have a 92 500SL and the fans do not come on when it is overheating.I replaced the thermostat but the old one checked out good anyway. I have wired around the S32 pressure switch and they will come on. I've check the B10/8 Sensor and it does get good readings. Does my jumping the leads around the S32 indicate that the R29 relay might be bad or the R15 resistor could be bad or both? My air conditioning has not worked in years and does not have coolant. Does that complicate the issue? Should the fans work with or without coolant in the system? Any thoughts?
Thank you. Let's sort this out together. The overheating is hard to visibly test, as the car's coolant has to be in the 110 Celsius range and getting to that range can be hard - does your car get to this level and you don't get the aux fans turning on?
By jumping round the S32 and having the fans turn on, means that the K9 relay is working and the fan connections\connectors work as they should. So your fans and the K9 relay are working. It could mean that the S32 is not functioning. The S32 is about protecting the AC - it's only one reason why your fans turn on. Since your AC is not working and has no gas, I would disregard going down the path of investigating or testing the S32. It doesn't matter for your situation as the S32 is about AC component cooling and not about engine cooling. Your worried about engine cooling, so I would focus on the B10/8 sensor and whether your car hits the temperature level required to turn the fans on. To trick the car into reaching temperature sooner, you can try adding a 1000 Ohm (1/4 watt) resistor to the B10/8 - just wrap the resistor wires around the two plugs of the B10/8 and put the wire plug back over it - and drive. You don't need to solder the resistor on. What this will do, is bring the temperature to a much more reasonable level (about 95 Celsius) to achieve, and your aux fans should turn on. The 1000Ohm resistors are very cheap. Let me know.
Note: Whether you have AC gas in the system or not, it won't impact the engine cooling parts of the aux fans.
Thank you again Val, so I have a dozen or so resisters on the way, think I will only need one,, haha, but that's how they sell them of course. In the mean time I was thinking why wouldn't jumping the connector at the B10/8 pins set the fans off the same as jumping them at the S32 connection? Essentially by putting the resister on the sensor lowers that threshold but if it gets to around the 250 or 300 mark and turns on the fan jumping them with a wire would send it to zero, shouldn't that make the fans run? I did try this but I get nothing? I suppose there could be a short in the wires somewhere, or could that mean the K9 relay on that side of the relay is not working? From the wiring diagram on the relay it looks to be two switches. Any thoughts? I did attempt to run it a little longer, a couple trips around the block but it did not go much above 85 deg. Nervous about taking it on a longer trip not knowing if it is going to overheat or not. @@HandyVal
James. It seems intuitive that the jumping of the wires and bypassing the B10/8 altogether should turn the fans on, but they won’t. I think it’s because it’s measuring the change or a level of resistance and zero isn’t an option - it’s puzzling because the jumping works for the others. Hey, if you struggle to get the car’s temperature above 85C, you likely have a fine tuned R129 operating at its best. It’s really in the stop and go traffic(and I mean heavy city traffic where one moves 1km in 10 minutes) that the car’s temperature hits the 90s. The additional resistor will get the fans to turn on at around 95 instead of 105/110C.
Thanks VAl, this has been so helpful, I have had to replace the fuel pumps/filter and accumulator as well as testing and cleaning the injectors it has been a real journey for me even though I have had this car close to 20 years now, I always took it into a shop for service, watching UA-cam videos has given me quite an education, the Benz fuel injection system was very state of the art back then. I am not a mechanic, but I was able to get it done. Thanks again for your help.@@HandyVal
Good stuff Val! I purchased what is called a "cool harness" it is resistor built into a fitting that goes on top of the 10/8 sensor. The wires then plug into this fitting. My resistor turns the fans on at 90c with or with out the air running. I live in the desert where temps on avg in june, july, august are 115-120F . Just driving to the store 12 miles away with only 1 stop sign my temps were running 100+c so it scared me and I bought this little unit 100 bucks for a .90 cent part. But it is worth it to me.
Thank you. You did the smart and right thing by adding a resistor and having the fans turn on at lower temperatures. Your engine will thank you by lasting much much longer than it otherwise would without expensive rebuilds. Anything over 100C for a prolonged and recurring period isn't engine healthy, even though some versions of the SL's operating manual does say it's the red zone on the temperature gauge that needs to be avoided. I haven't experience those outside temperatures you have yet, but in my summer months (outside temps 30C/90F) my SL's temperature easily sees the 95C (not quite 100C) in city stop and go traffic (where you move 1km/0.6miles every 5 mins), whereas on the highway it's in the mid to high 80C range (85-89), not quite 90. I will mostly likely use the resistor trick too. Thanks for sharing.
Thanks for the video! My issue is that only one of the fans is working on both low and high speed, should I assume that the other fan died?
Thanks for watching. Yes, the other fan has died, or it can be a broken connection. One fan on is always better than no fans on. It looks like the Mercedes engineers wanted at least one fan on because a basic electrical connection would imply that if one stopped working then it would break the electrical connection, so both would not work. Over-engineering wins this time!
@@HandyVal Thanks for replying
Now that you mention connection, I recently replaced the front bumper, hopefully I didn't forget to connect the fan 😀
@@peloponisios Yes. There’s a good chance a connection might have been missed.
good to understand how the whole thing works. Going to do my test now. I suspect the low speed is not working on my W201
Thank you. The video was inspired by questions I got on how the aux fans work. Let me know how your fans are testing.
@@HandyVal Followed your instructions to by-pass the high pressure switch, both the crutch fan and auxiliary fans works. Tested the relay, it works as well. My car when stop in the traffic the air conditioner is not blowing cool air. Any further testing can be done? thank you
Tested the temperature sensor on the head of the engine, without the engine is running, using multimeter. There is no reading between any of the 3 poles. I suppose it is a problem, am I right? But the clutch fan does run when the temperature reaches 100.
@@jackeywong6338 Thanks for doing this testing. It looks like the AUX fans and relays are all doing their job well. Your problem with the AC not blowing hot air has to do with the refrigerant gas - it has likely leaked out of the system. You can buy a kit at an automotive store and that would repump new refrigerant into your AC. There are many UA-cam videos on this - it does not have to be specific to the R129. The kits are fairly cheap, but you need to ensure you got the right refrigerant as there are different varieties. If the high pressure switch is green, as in the video I shared then you can use R134 refrigerant. A mechanic shop won't charge much for this service as well, as it's easy and a max of 30 mins work time. I hope this helps.
@@jackeywong6338 Sorry. I'm not following the 3 poles. Is this the blue sensor?
Hi Val, R129 SL500 fans turn on at stage 2 when I turn on the engine and fans shut off
when I turn off the engine.
Thanks for the comment. The stage 2 fans shouldn’t come on as soon as you turn the engine on. It seems like a previous owner/mechanic might have modified the fans to turn on all the time. If they were never coming on, then there’s reason to worry. What temperature do you typically see in stop and go traffic or after a 1+ hour drive? Can you see a resistor on the tab connecting to the blue coolant sensor?
when you take off the cap conector of blue sensor and when the engine is on, should auxiliary fan turn on automatically with the high speed?
They should not turn on. It seems logical that they should, but they don’t. Are your fans turning on?
@@HandyVal one mechanic told me they should be turning on, I tested and they several times it turned one once, but most of the time they dont. I am curious what is going on.
On some Mercedes models it does turn on when unplugged if the ignition is on. However not on the R129, as it’s set up differently. I think what happened to you, on the one instance they turned on, was that the friction of removing the plug tricked the resistance level to change within specs and that caused the fans to turn on. What model of R129 do you have?
@@HandyVal I have w126 (1989 year model) but it has m103 engine like yours, so most of the things around the engine is the same. Does outside temperature plays some role in that stage too?
For your model the fans will not engage if you unplug the blue sensor. The outside air temperature only plays a part for the low setting of the fans. The low setting does not use the blue sensor. So for your issue, the outside temp has nothing to do with it. How how hot does the car get in super slow traffic. I’d only worry if it gets consistently above 100C