The shop owner said the fan clutch spun after the engine stopped after checking the freon in my 89 420. He said the engine was probably getting warmer than normal due to the fan clutch weakness since it did not stop turning when the engine stopped. Said the engine was hotter so the AC switch was cutting off the compressor.

The electric fan comes on within 30 seconds of starting the engine. usually it would only run if the engine was hot.