On your car, does the aux fan stay on after the car is turned off. If not (as in my 87, 260E), the engine temp rises substantially after the car has been turned off. On my car, this would cause the activation of the coolant temp switch which cuts off the compressor. I am thinking, your car may be similar, so the compressor cuts off due to high engine temp after stoppage, but this temp has to be real high to cut-off the compressor and should not cut-off the compressor once the car begins to run and the engine temp has come back down again. So if such a temp switch is in your car, it is a bad switch, I would replace it and see if it fixes the problem.

__________________
Saumil S. Patel