low and high speed fans only not working when in heat mode on 1981 380sl
 

Hello fellow MB enthusiasts,
Im new here . I have a very nice 1981 380sl and have developed a fan blower problem . The automatic climate control high and low speed fan selections will not work in the heat mode but will work when the AC switch is turned on only . The fan also works when the defrost or bi-level positions are selected .If I go from the defrost or bi-level selections back to the high or low speed fan selections in the heat mode , they will blow for a short while and then quit never to come back on .Can anyone tell me what part needs replaced and where it is located ?
Kind Regards, Otto

Does this car have the push button HVAC controls? My 83 380 sedan had the push button controls which were known for cracking circuit board connections. These were relatively easy to repair when the unit was taken out and disassembled.

Does the 1981 still have the "Evil Servo" control system? I think 1982 or 1983 was the first year for the ACCII system. If so, do some research on the "Evil Servo" system, they're particularly problematic and very rarely work properly.