My W126 fan blower turns on after a while or, if at all, after a short to medium drive. I checked the blower directly with 12 volts, and the motor spins great.
Hi there. I am assuming that you applied 12VDC directly to the blower motor. If the blower motor started and ran full speed, then the motor is most likely not the issue. Often overlooked is the blade fuse for the blower motor. Make sure this one does not have a hairline crack in it. It has been known to cause issues like this. It sits in its own auxiliary fuse holder near the main fuse box. The next device that could be faulty would be the blower resistor. That is the spiky-looking thing mounted in the fan "box". It gets a voltage signal from the climate control and then provides the corresponding output voltage to the fan motor. They can go bad. With the max fan speed button pushed the voltage on the yellow wire on the blower resistor should be 6-9Volts; with the min speed fan button pushed the voltage would be around 1V. So if you do not get that voltage then the most expensive fault would be the climate control unit. So don't start there and check the other items first. Good luck.
On my 91 without passenger airbag you need to remove the door jamb trim and the rhs kick panel trim to get to a single screw that is hidden. There are three screws that hold the fabric knee bolster cover on that are easy to see. Also the resistor cover is sometime is a pain due to a power cord that might drop down unexpectedly. All of the covers should fit nicely without gaps. I had to fiddle with my junkyard find as the plastic grooves were bent up a bit. A good tip is to put a moving blanket (folded over) or something soft between you and the door jamb as you will be laying on it for about 30 ish minutes in w126 models. It's at best uncomfortable but not overly painful. It's a breeze compared to others where you have to remove the dash.
Ralph, bought the blower and resistor. Before I replace them did a last check up, replace the sensor on overhead light in front of Sunroof switch. The blower has been fired up without any issues. Go figure🤔😳
@@alc11803 Well, that would be wonderful if that fixed the issue. Trouble with old systems like this is that it could be just a loose wire connection that was somehow moved enough to make a good electric connection again. It could also be that the cabin sensor was the culprit although if I remember correctly heat or AC usually go up and down and with that the fan speed. Finally, I have had blower motors briefly come back from the dead status just to konk out again soon thereafter due to extremely worn rotor and brushes. Time will tell if you actually found the issue. The best of luck to you!
The old sensor I took out has so much black gunk inside the tube. Because after I replaced the sensor clean the pipe, turn the key and I can hear the Ambient motor hehind the passenger foot well. It's working perfectly, I thought there were delay because of the relay. Now the fan just goes right on within few second.
The core is a possible cause for no heat but not the most probable. Is the mono valve in working order? That is typically the top number one issue. If you have heat only at higher revs it is most likely the aux water pump behind the fire wall in the engine compartment. Good luck!
I really wish those Mercedes had a third fan speed, low speed is barely noticeable and high speed is far too windy and noisy, need another speed right in the middle.
Only the original MB visco coupling will achieve that middle of the road speed. The cheap replacement ones typically only go low or high with noting inbetween. Good luck.
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My W126 fan blower turns on after a while or, if at all, after a short to medium drive. I checked the blower directly with 12 volts, and the motor spins great.
Hi there. I am assuming that you applied 12VDC directly to the blower motor. If the blower motor started and ran full speed, then the motor is most likely not the issue. Often overlooked is the blade fuse for the blower motor. Make sure this one does not have a hairline crack in it. It has been known to cause issues like this. It sits in its own auxiliary fuse holder near the main fuse box.
The next device that could be faulty would be the blower resistor. That is the spiky-looking thing mounted in the fan "box". It gets a voltage signal from the climate control and then provides the corresponding output voltage to the fan motor. They can go bad. With the max fan speed button pushed the voltage on the yellow wire on the blower resistor should be 6-9Volts; with the min speed fan button pushed the voltage would be around 1V.
So if you do not get that voltage then the most expensive fault would be the climate control unit. So don't start there and check the other items first. Good luck.
You are an absolute Rippa mate , good onya cobba
Thanks, man.
On my 91 without passenger airbag you need to remove the door jamb trim and the rhs kick panel trim to get to a single screw that is hidden. There are three screws that hold the fabric knee bolster cover on that are easy to see.
Also the resistor cover is sometime is a pain due to a power cord that might drop down unexpectedly. All of the covers should fit nicely without gaps. I had to fiddle with my junkyard find as the plastic grooves were bent up a bit.
A good tip is to put a moving blanket (folded over) or something soft between you and the door jamb as you will be laying on it for about 30 ish minutes in w126 models. It's at best uncomfortable but not overly painful.
It's a breeze compared to others where you have to remove the dash.
Thank you, Richard. That is a very nice description and very helpful.
I can not thank you enough. I have to do this job asap. My fan just failed
Good luck to you replacing the fan.
About to embark on this adventure 89 560 SEC
Good luck to you
I’m replacing the motor brushes on my 1991 w126 thank you 🙏
Glad it helped.
Ralph, do you know is it the same blower motor in my 87 300sdl? I'm ready to purchase one to replace mine. Thanks
Yes, that one is the same. Good luck.
@@straybenzes I'm getting one blower motor with resistor from 1991 350sdl. Thanks
Ralph, bought the blower and resistor. Before I replace them did a last check up, replace the sensor on overhead light in front of Sunroof switch. The blower has been fired up without any issues. Go figure🤔😳
@@alc11803 Well, that would be wonderful if that fixed the issue. Trouble with old systems like this is that it could be just a loose wire connection that was somehow moved enough to make a good electric connection again. It could also be that the cabin sensor was the culprit although if I remember correctly heat or AC usually go up and down and with that the fan speed. Finally, I have had blower motors briefly come back from the dead status just to konk out again soon thereafter due to extremely worn rotor and brushes. Time will tell if you actually found the issue. The best of luck to you!
The old sensor I took out has so much black gunk inside the tube. Because after I replaced the sensor clean the pipe, turn the key and I can hear the Ambient motor hehind the passenger foot well. It's working perfectly, I thought there were delay because of the relay. Now the fan just goes right on within few second.
Where is the actual heater core on this car? I have NO HEAT. I think the blend door is stuck closed.
The core is a possible cause for no heat but not the most probable. Is the mono valve in working order? That is typically the top number one issue. If you have heat only at higher revs it is most likely the aux water pump behind the fire wall in the engine compartment. Good luck!
@@straybenzes monovalve has been rebuilt and heater core has been flushed. Hoses to/from monovalve are hot. I have no heat at any RPM.
I really wish those Mercedes had a third fan speed, low speed is barely noticeable and high speed is far too windy and noisy, need another speed right in the middle.
Only the original MB visco coupling will achieve that middle of the road speed. The cheap replacement ones typically only go low or high with noting inbetween. Good luck.
WD40 help
It does help for a short while. Liquid lube does not work in the long run though.
@@straybenzes I agree, you need a good lubricant. WD40 it is good to wash off dirt
Then inhale the chemical fumes for a while.