Mr Benz, I have exactly the problem you describe with the a/c on my '87 190D. When the dehumidify button (the one above the AC) is pushed, I get cold air (w/ compressor engaged) from center vents, but hot from outer. With AC button depressed, compressor cuts out after about 45 sec.
So I'm curious what you found out about your problem. Any answers from anybody? TIA
Oh, and thanks to Benzmac for help with vacuum control valve. Changed it today, and for the first time, the tranny shifts SMOOTHLY! Thanks.