W124 heat climate control - PeachParts Mercedes-Benz Forum

clar683 · #1 03-22-2004, 02:27 PM

I just purchased a 1990 300TE to drive during my stay in England. It has the climate control system with the dials (blue/white/red in color). The heat is constantly on, and won't turn off, regardless of the settings. On long trips, it sometimes will stop, but for local driving there is only hot air. Is this a vacuum problem? Please advise.

psfred · #2 03-22-2004, 10:47 PM

Temp control dial with a row of buttons?

If so, does the heat come out the floor and side vents or just out the base of the windshield?

The system defaults to full heat without blower, defrost (windsheild vents only), no blower if there is no power, so if this matches your condition, check the fuse! Gets rather warm in there with a bad fuse.

If the blower runs, it's not the fuse, but could still be the monovalve. The valve is held closed by applying current, so if it's bad, it will fail open, causing full heat. If the blower changes speeds and the air flow comes out different vents depending on interior temp, the monovalve is likely bad.

Most other problems are the pushbutton unit itself.

If it's the manual system (one dial for airflow, two for temp, and blower speed buttons?? -- never seen one in the US), I believe the temp is still controlled by some sort of electric valve, doubtless failed on your car.

Peter

Peter

TROVERMAN · #3 03-23-2004, 01:07 PM

My UK spec E320 wagon (1995) with auto climate control (I believe you are talking about the semi-manual system which does have seperate temp controls for the driver & pass) had a similar problem--check in the area of the fusebox and brake master cylinder area when the car is running. See if you hear hissing vaccuum. There are several lines and valves (yellow) which interconnect here. Good luck

clar683 · #4 03-23-2004, 06:18 PM

It is the semi-manual system, which does have separate controls for driver & passenger. I believe it is a vacuum problem. I'll check for hissing sounds. How did you repair yours?

clar683 · #5 05-26-2004, 03:53 PM

Could not hear or locate any vacuum leaks. The heat still has a mind of its own, and turns on even though the dial is set to cold. I believe it to be a vacuum problem because as soon as the car is up to highway speeds, the heat turns off. Apparently, it is taking time to build up enough vacuum.

Any other suggestions? Alternatively, is there a way to simply disconnect the heater for the summer? At Mercedes-Benz labor rates here in England at $200 per hour, I would like to resolve this problem myself.

In advance, thank you.

TROVERMAN · #6 05-27-2004, 08:22 AM

The problem mine had was with one of the yellow vaccumn motors near the master cylinder (opposite side of the car for you?) It cost me $7.50 US and has fully solved the problem. By the way, the car generates maximum vaccumn at idle. As for other suggestions, try this: remove the wood center panel which houses the climate dials. There are two screws right above the radio on the bottom of the panel. Once these are removed just carefully pry out ot panel. Then remove the climate control unit (There are a bunch of small silver screws set in the black plastic for this) Once the CC unit is out, you should see a good-sized vac. motor with a connecting rod on one end and a hose on the other end. When you take the CC out, don't unplug it. Start the car, and put the CC on a cool setting. If it blows heat (do this when the car is still warm), try grabbing the rod on the vac motor and moving it one way or the other. See if this makes a difference. Alternately, by the nature of your problem, could it be the overhead sensor located near the sunroof switch? Worst case scenario is that it is the CC Unit itself. Good luck.