W124 HVAC temperature sensor fan R&R - PeachParts Mercedes-Benz Forum

Chris W. · #1 12-12-2010, 11:12 AM

Yes, that pesky fan which draws air from the small overhead grating in a 124, to allow the cabin temperature to be sensed for the HVAC system. I pulled the fan out yesterday to lube it, because with the cold weather it was squealing badly, sounding like it was about to die an ugly death and let the smoke out.

What a PITA. First take the air bag out. Refer to other posts on the Board for this, but please be safe. I thought I'd be able to see the fan in plain view, but no. Where is it? Thought of hooking up the battery again and energizing the HVAC system to hear the squeal, but I did not want to do that with the air bag out of the car. So I researched some more and found a post which said the fan was up under the right side dash speaker.

So I took that out. No real joy, keep looking. Turns out the sucker lives just under the vent, and under the large diameter vent duct pipe. It is held in a big block of ratty foam rubber, which in turn is held in by a couple big metal clips. I suppose to lessen the sound and vibration transmitted. I wound up taking apart the airbag mounting frame to have better access for my hands to reach over and get at the fan.

The small duct pipe can be pulled off the fan, and the fan can be pushed towards the front of the car without taking the foam rubber block out. Just grab the fan and twist/pull it forward, and push from the back side. The back side (towards the back of the car) has the electrical plug. Eventually you can work it out of the foam block, and disconnect the electrical plug.

But now there is no real dis-assembly you can do to the fan itself. You can pull off the plate with the electrical connections, but it doesn't help you see the bearings. And you can pull off the end plate on the fan side, but no real help there either.

I just blasted the whole thing with electrical contact cleaner, then aired it out, and then shot it up with some spray lube I have for bikes and things. There is a small gap between the fan and the body in which you can aim a spray tube. I didn't have a 12V source on my workbench, so I used compressed air to spin the fan while blasting it with lube.

Assembly is the reverse of removal, as they say. I will have to wait for a cold morning to see if it really helped.

One bonus, however. There is a vacuum line distribution block which controls which HVAC vents open, I believe, which is visible when you take the airbag out. You can see it on the left side of the opening. Turns out that the bottom two vacuum lines were disconnected from the block! (lines are color coded) Could be the reason for the weak flow I've had from my center vents. Another PITA to reconnect those lines, but I succeeded, using some surgical clamps and long screwdrivers.

I shudder to think of the labor cost for R&R'ing the tiny fan at a shop. And no way they would have seen those disconnected lines. All in all, a satisfying afternoon's work.

Rgds,
Chris W.
'95 E300D, 331K

Jeremy5848 · #2 12-12-2010, 01:02 PM

Well written. My '87 300D Turbo (W124, OM603) also had a noisy fan and worse, the early 124s mounted the fan on the under-dash panel, which acted like a drumhead.

I discovered that later 124s use a bracket mounted on the cross-chassis brace so I adapted one for my car. The fan now is so quiet it can be heard faintly and only before the engine starts.

The '87 has no passenger airbag so operations are easier.

Jeremy

dablk1 · #3 12-13-2010, 09:37 AM

You should have been able to open up the housing and remove everything.

Tpawlik · #4 12-17-2010, 10:43 AM

My fan is running because I hear it, but the sensor is not "talking" to the push button unit.The pushbutton unit is a newer known good one, but it is operating the same as the original one. I saw and downloaded the ohm values to check the sensor. Does anybody have a picture of the sensor removed? Do I check the ohm values across the two wires or on one wire and a body ground?
Thanks.

dablk1 · #5 12-17-2010, 01:17 PM

Across the 2 wires.