86 turbo quattro avant; climate control not working.

["Bruno Cantieni" <brunoc@interlog.com>]

Periodically and for no apparent reason, the climate controll would shut
off. (No display, no functionality).
Shutting off the engine and restarting would usually get it going again.
Recently the climate control dropped out again, but this time for good. The
only thing working is the illumination when the lights are turned on.
I checkd the obvious, such as fuses and relay but these appear to be
funcioning.
My local mechanic (good with, but not highly specialized in Audis) spent two
hours looking for possible problems and in the process exchanged both the
climate control unit as well as the computer (behind glove box) with known
working ones, alas to no avail. I checked the archives and found no answer
to this one.
Any ideeas would be greatly appreciated before I take it in to the dealer
and face spending god knows how much money.

Bruno Cantieni