PeachParts Mercedes-Benz Forum - View Single Post

wgilmore · #2 05-24-2008, 04:59 AM

The wonders of old technology. There are guys on this forum who are extremely well versed in the AC systems on these cars much more so than than I am. Hopefully they will post a reply.
However I'll put my 2 cents worth in for you.
From what you write , it sounds as though your compressor is engaging and functioning and then disengaging at high speed 70Mph , like 2700 RPM.
Does your AC function correctly and continuously for extended periods at low speeds like 40 Mph. ?

You might start by looking at the items below.

Compressor speed sensor failure at higher RPMs. Compressor speed sensor signal must sync with tach signal at correct ratio. Belt slippage from water or whatever can cause this.

Low (or low/high)pressure cutout switch (very unlikely, but happened on my Swedish car) where the pressure is getting low enough to switch off the compressor. Pressure may as well be too high cruising - not normal though.
Pressure would usually drop when you have good airflow across the condenser.

Tach signal failure from EDS. Required to start the compressor.

Klima relay failure (they are called this but really are logic based ).

Over temp. cutout switch (cuts out at 120C). Was your temp getting high?

Control module ( the one in the dash with push buttons and temp wheel).

Evaporator temp sensor old and out of range since last year - probably not, but may be an issue since it is I believe an NTC thermistor.

Clutch on compressor going bad. You know, it's magnetic , gets hot , fails, cools down , works... etc.

There are just a number of things that could cause your system to stop cooling. There is probably someone on this forum who has experienced this same issue. If you have more info , might be helpful.