I have a problem with the A/C Fan not running on my 1992 400E. I have searched the Climate Control groupings and found several possibilities. I want to see if there are other suggestions or things that are more likely. This happened to me once before where the fan did not run at all and it was the fuse strip (separate from the fuse box, but close by) that was blown and that I replaced. That fuse seems intact now.

Othere possibilities that I have found:
* Fan motor itself - before it stopped running completely, I occasionally got a squeal from the fan while running
* Fan switches and control board - solder joint or connection problems
* Auxilliary fan? - unclear on this one

Any advice would be appreciated on best order of attack.

Thanks,
Kim

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1992 400E (W124) - 177K Miles - fun car!!

Change the fuse, even if it looks OK. If that doesn't fix it, it could be the brushes are worn out in the fan it self. Search on this site for brush replacement. I think there might be a DIY.

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Check for voltage at that same fuse strip. If there is none there, you need to back up through the system and find the problem. If there is voltage, then I'd put an ammeter in line at see if there is any power consumption at the fan. Probably "zip" due to worn brushes, esp if it's been noisy lately.
It's a bit of a bear to change. Go with a new Bosch motor, it's tough enough to get to without putting in a lousy reman part. You might be able to find a new one without the squirrel cages, that's the best deal if you can find it. The you can put the old squirrel cages on a new motor.
Gilly

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Open hood to full position.
Three wire connector on the firewall, behind booster.
Red/Blk/Yl

That is test connector point to blower/regulator:

Key ON , ACC to Defrost.
You want to see 12v across R/Blk...and variable V [ 2-9V.] from Yl to Blk , depending on ACC setting..The R/Blk are 12v feed and the Yl is trigger sig to regulator for speed control. If YES to both test , the problem is downstream from the connector [ meaning down at the blower/regulator.]
If NO , then the prob is upstream from connector [ meaning fuse , ACC panel, etc.] This test point is used b/c it seperates the cabin controls from the engine compartment circuit. [ making diagnosis simple, as it is a circuit mid-point and easy to get to]
Finally, if YES at test, then go to blower and ground the blu wire @ blower with a jumper to ground ..if the blower then starts , the prob is the regulator...if NO , it is the Blower [ brushes, frozen bearings , etc]
That's it.........

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A Dalton

Thanks Arthur. This is a very useful test that I did not know about before. This 3-Wire connector you refer to is behind the brake vacuum booster? Does it have a cover or other way to identify it?
THanks

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1992 400E (W124) - 177K Miles - fun car!!

It should be way up on the firewall , behind the booster section..that is why I mention full hood ..
Just look for a 3 wire connector with those colored wires.................. those wires all go down to the blower compartment.
Which is why we use that connector before pulling everything apart. [ X/64 connector]

If you can't find it on that chassis , I will look it up in the Location Pictorals

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A Dalton

I just did this on a 1990 300TE, wife says the blower motor is running slow so I drove it and determined that the blower motor wasn't running at all. As the motor was suspect anyway I went ahead replaced the blower motor assembly. Not easy, but not too hard. At anyrate, sure nice to have a furnace in the old wagon again.....here's my list of parts and price to resolve this thing possibly (if you are interested).....80 amp fusestrip for blower motor $3.00 from Mercedes Benz themself, didn't work. So what I did was went out to a U-Pick-Em salvage yard and found a killer example in a 1993 300e sedan. I pulled it and it was $15 and it works great. As a result it cost me a sum total of $30 to replace an otherwise not working blower motor assembly...not Bosch though...it's Behr.....this could of cost $400 instead of $40....be careful my friends

I do have voltage at the fuse strip: touching a volt meter to either side with the other probe grounded to the frame gives about 14V.

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1992 400E (W124) - 177K Miles - fun car!!

<).....80 amp fusestrip for blower motor>

I am going to assume that to be a typo.....................................

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A Dalton