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Old 12-18-2010, 02:14 PM
Registered User
Join Date: Dec 2005
Location: Streetsboro, OH
Posts: 245
Cabin Temp. Sensor and Fan Problem

My heat is either all on or off. I installed a known good CCU and the heat is the same. Thanks to a timely write up by Chris W from the gasser forum, on how to R&R the fan, I tried placing a square of paper against the sensor grille. Nothing. Earlier this week and in the past, I could here a motor running while waiting for the glow plugs to do their thing, so I was pretty sure the fan was working.
Yesterday and today, no motor sound. So, when I find the fan hiding under the vent, the rubber hose is disconnected and when I powered the fan, it ran silently. I removed it and split the case. I put a couple drops of 3 in 1 oil on the shaft. Figured it couldn't hurt. I spliced on some extra hose to make it easier to put back. When I tested the motor again before installing it, it made the same noise I had been hearing, The impeller was lightly touching the housing. I was able to slide the impeller a little to get the needed clearance.
It is silent again and will hold up the little square of paper.
I haven't driven the car yet. I would really like to start running the heater with the temp wheel, instead of the Off and Economy button.

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
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Old 12-19-2010, 12:18 PM
Jeremy5848's Avatar
Registered Biodiesel User
Join Date: Mar 2006
Location: Sonoma Wine Country
Posts: 8,394
The little fan "encourages" the temperature sensor in the overhead to respond more quickly to temperature changes in the cabin. It [the fan] is unlikely to be directly connected to your problem.

As a start, remove the dome light assembly and check out the electrical connections to the temperature sensor. If one has broken or come off, the temperature sensor will not be able to talk to the CCU and the temperature dial will not work. The result will be the symptom you describe -- full heat with the dial set all the way to the click stop at the high end and no heat otherwise.


"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
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Old 12-19-2010, 04:20 PM
Gilly's Avatar
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Join Date: Mar 2001
Location: Evansville WI
Posts: 9,616
Possibly could be a weird failure of the mono water valve, depending on the exact failure they can give all sorts of different complaints. Doesn't cost anything to check it.

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