I have a question about my 1985 300D. My a/c compressor is cutting out at idle and at low cruising speeds. If I put the car in neutral and rev the engine up to at least 2500 rpm, it turns back on. The tach is not affected when this happens. I was thinking it could be the Kilma relay (since this a/c compressor doesn't have a speed sensor I am not sure what the Kilma relay's purpose is. The wiring diagram on my cd rom manual looks like a bad photocopy and is useless), the ovp relay or something in the acc itself??. When it is working, it is like a meat locker inside the car. Just thought I would bring this up to see if anyone has had similar experiences on this year/model 300D.

Have you checked the freon pressure? I don't know much on the specifics on the MB air conditioning system (I haven't had to deal with it yet *knock on wood*), but many systems have a cutout to kill the compressor if there isn't enough pressure in the system. Maybe at higher RPM's, it gets enough pressure up to operate...

Just a thought...good luck!

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2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999

Refrigerant pressure is good, it was converted to 134a and when the compressor is working it will get very cold for a converted system (high 40's to low 50's coming out of the vents after it has cooled the interior down). Seems more like a voltage related problem. The auxillary fan comes on when it should. It will stay running after the problem causes the compressor to cut out since there is hot refrigerant in the line where the fan switch is. I guess I could have a bad pressure switch. I will check it in the next hour. If that is the problem, it will be a PITA since the system must be evacuated, recharged............$$$$

Actually, with a 134 system, you should be able to recharge it yourself. You can get a recharge kit and bottles of the refrigerant from an auto parts store. That still leaves evacuating the system, though...and evacuating it again after installing the new pressure switch (if memory serves, you're supposed to have total vacuum in the system before installing the refrigerant).

There may be a way to test the pressure switch for proper operation; I'm sure someone will chime in with the procedure to do that, if it exists...may be a good idea to do that before evacuating the system.

I checked the pressure switch. No power is getting to it. At first I just bypassed it with a jumper wire, then checked with a VOM, nothing there. I jumped the compressor to the battery and it came on, so the compressor clutch is good. I rehooked it back up, raced the engine, and it came on immediately, then shut off after about 30 seconds of idling. I am leaning towards a bad Kilma relay, or temperature controller about the glovebox. I have ordered, from a fellow member, a good used pushbutton unit and wood faceplate because mine looks worn and the faceplate is cracked. If the snailmail ever delivers my payment to him, he will ship it. (should have fed-exed it I guess) I don't think the pushbutton unit is the problem, everything else works great. I just get weird looks when I rev my engine in traffic so I don't start sweating at a red light.

There is a way to set up a fused switch to supply power through the evap freeze protection switch which will put power to the pressure switch at the dryer and on to the Klima relay. You can just turn this switch on or off as you want the compressor on. The pushbutton unit can continue to be used to operate the vent doors and the fan speed.

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Jim