GAKFU,
It took a minute to find you have a 88 944, you might want to upgrade your "User CP" on top. Edit your signature to let us know what you have.
anyway...
Tidybouy is correct. Your car is low on freon. To check if the compressor is getting voltage, there is a single wire that comes off the compressor. Unplug it about 2 feet along the frame and with the key ON-(not started) and the AC switch ON----the wire should have 12V tested with a Volt meter.
You could also jumper the safety switch ( a 3 inch wire with 2 female ends) mentioned above by the receiver/dryer for just a few seconds and see if the compressor kicks in.
Then read about converting from R12 to R134a:
http://www.the944.com/
GK
John