PeachParts Mercedes-Benz Forum - View Single Post - 1990 300E A/C suddenly stopped blowing cold

Benz Mondi · #8 06-21-2015, 01:05 AM

Replace the MAS and all is good and cold again!

This was the first MAS failure I experienced with all the 1990-93 MB's I had (5 at various times).

Recap of symptoms and diagnosis:

1. Car always had strong a/c, suddenly stopped being cold when I got back in the car after an appointment on Wednesday. It was 97 deg. outside.
2. Clutch could be spun by hand with only a light amount of resistance and did not feel loose.
3. To check if Freon (still using R-12) was too low, bypassed low pressure sensor and jumped the two leads, with the a/c power on and the engine running.
4. Confirmed with multi-meter that 12v was present when the two leads were connected.
5. Inspected plug and wiring attachment at side of compressor, no apparent issues.
6. Replaced MAS is my 1990 car with one from 1991 (could not find the exact part number match from the salvage yard), a/c is functional again.
7. Car is not throwing any DTC's (diagnostic trouble codes).
8. Added 1/2 can of R-12 with dye for leak detection as abundance of caution.

Thanks for all those that chimed in their help.

Done!