weird a/c behavior

[Rokas Reipa]

Hey everyone. Been trying to figure out why my a/c has been behaving the way
its been the past few weeks. The car is a 1993 audi 100s with manual climate
controls and R-134 from the factory. To start off, the a/c cools the
interior great; no problems there. The first problem is that sometimes, it
is not possible to shut the a/c off after its been running for a while. The
button can be pressed at will but the a/c light is still illuminated and the
a/c continues chugging away. Secondly, the fans sometimes start running at
high speed when a/c is turned on and stay running at high speed the whole
time the a/c is on. The whole car shakes and vibrates as a result. Third,
the a/c compressor does not appear to be cycling at all. I was going to
check the freon level; is there anything else that needs to be checked to
alleviate some/all of these problems? Thank you in advance,

Rokas
93 100s