A/C Fan not running on 1992 400E - PeachParts Mercedes-Benz Forum

parnelltk · #1 03-29-2009, 06:35 PM

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

Bio300TDTdriver · #2 03-29-2009, 07:14 PM

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.

Gilly · #3 03-29-2009, 07:48 PM

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

Arthur Dalton · #4 03-29-2009, 08:30 PM

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.........

cliffmac · #5 03-29-2009, 08:39 PM

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

parnelltk · #6 03-29-2009, 08:40 PM

Quote:

Originally Posted by Gilly

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

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.

Arthur Dalton · #7 03-29-2009, 08:43 PM

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

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

parnelltk · #8 03-29-2009, 08:43 PM

Quote:

Originally Posted by Arthur Dalton

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.........

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

Arthur Dalton · #9 03-29-2009, 08:47 PM

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

parnelltk · #10 04-04-2009, 04:25 PM

Quote:

Originally Posted by Arthur Dalton

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

Thanks Arthur. I have been away and just had a chance to look for the connector. I think I found the right one, behind the booser and a little higher. It is a tight squeeze for a hand. So I got the connector separated. The block that stays on the firewall has 3 pins that correspond to the Red,Black,Yellow wires on the connector.

First question: I believe these pins at the connector block on the firewall are where I should check for voltage, right? The wires on the connector that I can pull out I believe go down to the fan.

Second question: If the pins back on the firewall are the right place to measure voltage, what is the best way to connect to them? It is tight, so is a clip best?

Thanks!

Arthur Dalton · #11 04-04-2009, 05:41 PM

You can usually slip a probe into the connector along side the wires w/o unplugging it. You can also use a good ground for the Blk...or even a test lamp probe will do. Your main concern is that you have 12v at Red and a voltage sig at yl.
The firewall plug is power feed side and the connector/wires goes to the blower/regulator, so if you do unplug it , you check at the plug that stays on the friewall.
If you have power at both R and Yl, with blk being used for ground on both test, then the ACC supply side of the circuit is OK and the prob is down at the blower..meaning you then have to dig down in there ..that is why you do the test at this convienient test point first. You do not want to go to the trouble of dismantle to get to the blower/reg , only to find out the problem is Upstream......
Many a DIYer checks the fuse and then decide it must be a problem down in the blower compartment, only to find out there is no variable V at the yellow wire..which is the trigger signal to switch the regulater ON..w/o that sig, you have NO Blower ...so that is as important a test as the Red 12V one.... an often mis-diagnosed condition.