Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help

Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Tech Help

LinkBack Thread Tools Display Modes
Old 12-12-2010, 11:12 AM
Registered User
Join Date: Jul 2001
Posts: 898
W124 HVAC temperature sensor fan R&R

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.

Chris W.
'95 E300D, 331K

Objects in closer are mirror than they appear.
Reply With Quote
Old 12-12-2010, 01:02 PM
Jeremy5848's Avatar
Registered Biodiesel User
Join Date: Mar 2006
Location: Sonoma Wine Country
Posts: 8,394
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.



"Buster" in the '95

Our all-biodiesel family
1995 E300D (W124) . .239,000 miles My car
1996 E300D (W210) . .313,000 miles Wife's car
Santa Rosa population 170,685 (2012)
Total. . . . . . . . . . . . 722,685
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
Reply With Quote
Old 12-13-2010, 09:37 AM
Join Date: Dec 2007
Location: Maryland
Posts: 508
You should have been able to open up the housing and remove everything.
1995 E420 152k
1991 300D 2.5 348116 daily driver
1992 300E 2.6 196k-work in progress(head gasket)
2002 BMW 745Li 93k
Reply With Quote
Old 12-17-2010, 10:43 AM
Registered User
Join Date: Dec 2005
Location: Streetsboro, OH
Posts: 245
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?
1987 300D 146K Original #14 Head
One eye on the road, the other on the temp. gauge

Gone But Not Forgotten
1983 380 SEL Long gone
1983 300SD Wish I hadn't traded it in on a 90' Corvette
1989 300SE My all time favorite
1995 E420 Went like a bullet
Reply With Quote
Old 12-17-2010, 01:17 PM
Join Date: Dec 2007
Location: Maryland
Posts: 508
Across the 2 wires.

1995 E420 152k
1991 300D 2.5 348116 daily driver
1992 300E 2.6 196k-work in progress(head gasket)
2002 BMW 745Li 93k
Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 08:22 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page