I had a similar problem with my 92 500SL. Here is the thread where we went through it.
http://www.peachparts.com/shopforum/showthread.php?t=218902
There is a sensor on the rear of the compressor that senses if the compressor shaft is indeed turning once the clutch is activated. If it doesn't see the pulses from the sensor coil in a couple of seconds it will cut out for safety purposes...
Some of the wires used in the wiring harnesses for 92 and 93 models had insulation that would become brittle and fall off resulting in shorts when exposed to heat over time.
Take a look at the wire harness that starts at the rear of the compressor and runs to the front and joins the plug with the wires to the clutch. These leads are probably brittle and BARE.
To fix this you can just replace the sensor, but you will have to evacuate and recharge the system. If the compressor is still original, you might as well just replace the compressor like I did and go on with life...