Thanks for the positive feedback.
I have one more possible cause to toss in: the serpentine
belt is slipping, causing an actual difference in speed
between the engine and compressor, which the Klima relay
is correctly detecting. There are two possible causes
of this particular malady: An old, stretched, or greasy/
dirty belt. Also, the belt tensioner is occasionally
known to fail. The original tensioner design on these
80s diesels had problems, they all failed. It was replaced
with an upgraded version. It's possible this is the cause,
but in all liklihood the tensioner has been replaced on
these cars a long, long time ago.