Well Charles, we probably should start a separate thread on your car as its causes are so different from the pattern failure I threw out for the 81 car.
The characteristic symptoms of no heat after the car starts driving in the later Klima system makes the Monovalve capsule a low risk call. On your system the lack of heat is likely to be that the servo/heater valve is not opening. That can occur for a number of reasons. One diagnostic observation is to see if the center duct changes during a change from the coldest setting to the hottest. Airflow should gradually stop as the heat mode is engaged.
If this occurs then you probably have a bad servo as the same action of the servo will normally open the water valve as the internal vacuum distributor moves to change the ducts.
If there is no change, then I would either suspect a locked up servo and/or an inactive controller/amplifier (behind glove box).
The servo has a clockwork mechanism inside that is driven back and forth in an electronic balance by a small motor driven and monitored by the amplifier. The teeth of the gears commonly break cuasing it to jam. With the motor unable to move the amp is overloaded and often is taken out by the first failure.
One of the neatest tools my brother (the electronics nut) built for us years ago works wonders on this system (we should have sold it to MB). It inserts in series electrically into one of the connectors at the servo (one connector is all inputs and activities and the other is blower control). It has a green LED and a red LED showing us the polarity of current through the internal servo motor (this shows whether there is driver motion either in the hot or cold direction), it has an analog meter that shows the feedback potentiometer reading (this tells the position the servo is in - heat being all one way and cold the other). There are a couple other signals, but the best thing it does is allows the operator to over ride the amp signal and manually control the servo.
Since he built it we have only had vacuum problems with that system. Electrical problems aren't.
Bosch Master, ASE Master, L1
33 years MB technician
Last edited by stevebfl; 11-10-2001 at 08:51 AM.