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HGV 03-31-2020 12:04 PM

W124 Climate Control System
 
My 1995 E320 wagon has never had a properly functioning climate control system. I decided to get to the bottom of this. This was my wife's daily driver and she used to call the car menopausal. Either too hot or too cold.

I started with the vacuum system. I removed the passenger side air bag. Very easy with one bolt removal from under the dash. Two electrical plugs and the air bag is out of the way. Don't start the car with the air bag disconnected. I have heard that the SRS light will stay on. I removed the mounting hardware as the vacuum solenoid switch is difficult to access. The switch is held in place by plastic prongs. I found that if you twist it counter clock wise, it unsnaps. All the vacuum lines are color coded so it is easy to put back together as the switch is also color coded. Used a mighty vac and checked all the pods. Foot well flap vacuum line had pulled out of the pod. I removed the push button controller and reinserted the vacuum line.

Then i checked the vacuum lines near the brake booster. Found a leak to the vacuum reservoir. I plugged that line . Still need to find that leak. There is a vacuum reservoir located in the passenger side fender. need to get at it by removing the wheel well access panel. Save that for another day.

Once all the vacuum leaks are solved. i reinstalled the air bag and went for a drive. Still climate control not functioning.

Decided to trouble shoot the monovalve. It is located near the battery. I wired a test light from the two prongs into the car. Went for a drive. The valve is fail open, energize to close. It cycled but could not maintain consistent temperature.

Decided to check the cabin air temperature sensor. First i checked that the sample air blower was working. Removed the air bag. It is located under the passenger side cabin vent. With the air bag removed and the duct removed, you can access the blower. I could feel the fan turning with my finger. Turned the key on and it spun right up. I had tried the test of plugging the grill near the dome light with a piece of paper, but i could never get a good sense that it was working. A piece or saran wrap would stay in place, but never had a good feeling.

Removed the dome light housing. It is held in place by spring clips on the passenger side and hard plastic clips on the driver sides. Removed the air hose and then pried out the temp sensor. First thing i noticed is it was partially plugged with years and years of dust. Cleaned it all out and connected it to an ohm meter and confirmed it works.

Put is all back together, reinstalled the air bag and went for a ride. Still no decent control. Next was to check the heater core temp sensor. It is located behind the push button controller. Went to find it and it was missing. It was dangling behind the radio, attached to the wiring harness. Reinstalled the sensor. Put everything back together. Went for a drive. It all works. This has been an ongoing problem since i got the car new. Dealer could never fix. Probably it fell out during car assembly.

After all these years the system now works.

Couple interesting things. The mono valve stays mostly closed. Only times it stays open is when the defrost is on or when the temp dial is set to max. Also when the car is cold. It stays fully open until the heater core sensor has heat and then the fan starts on slow. From there on, it cycles open for no more than a second or two.

Just wanted to share this experience. I have the climate control trouble shooting manual. It is from 1992, my car is not covered, but these systems are all the same on these cars.

HGV 03-31-2020 12:31 PM

Some photos
 
3 Attachment(s)
Some photos of the dome light area

wolf_walker 03-31-2020 04:02 PM

Good job, I've been through most of this at one time or another, but never all at once such that the thing actually works completely correctly. :)


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