For now, forget the freon issue. The low pressure cut off switch will work even when undercharged moderately. Since the problem started with an engine wash, I'll bet your Klima relay is wet (and hopefully not fried). Check Klima on fender well, drivers side, sorta right behind headlight. Check this and see picture here: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)