I had the same issue with my ‘96 G320. Everything checked out (as far as Freon charge, fan switches, etc). I thought I was having an issue with the main control relay, so I started checking all the inputs and outputs. Everything looked good here as well except for one input. I believe only the the 463 had this feature, but it turns out that the a/c compressor has a rpm sensor (on the back side , opposite the clutch) that measures the difference between engine rpm, and compressor rpm. If any differences are detected, the main control relay reads this as a sign of belt slipping, therefore cutting out the compressor. Most times, you can just turn the ignition off, then restart the car, turn the a/c back on, and all is well. Turns out my compressor has a bit of a hard spot sometimes, which kicks in this safety feature. New compressor solves this. Hope this helps.