A/C problem with Brunhilde, the 1991 745 Turbo SE.

Last summer the A/C compressor would sometimes run for long trips, sometimes would cycle on and off, only running for seconds each time. I had feared a Freon leak, but shop could not find one with dye. I also feared crud in the plumbing that would randomly plug up the orifice. The shop did not check A/C system pressures.

This summer, same thing, but with added twist of choosing to blow air out of which ever set of ducts it wants to, at random. Also seems to turn on a small amount of heat at times while playing musical ducts. This seems, to me, to be pointing to a problem with the MCC unit (manual climate control). This car's MCC is the one with three knobs and the two push buttons. It was replaced in July 2003, nearly 7 years ago, by the previous owner.

Does this seem like it is more likely the controller than the freon system to you guys?
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1955 Human, Scott; 1991 745 Turbo, Brunhilde; 1990 745GL, Snuggle Bunny