Steve Brotherton speaks of the compressor speed sensor on the back of the compressor on some models. It's purpose is to let the MAS compare engine speed to compressor speed and disengage the compressor if there is a difference above a certain limit, thus preventing a broken belt. Because of the RPM craziness at compressor disengagement, I'd at least look into this protective circuit. May help, may not. FWIW.

Steve's article:http://www.peachparts.com/Wikka/AcDiags

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)