Am I correct in my understanding that the servo is for heat and the compressor is for cold air? I haven't been able to get either working, but this might also be related to my vacuum system in addition to the York being beltless and zip-tied. The wiper fluid squirt, door locks and shutoff have never worked. Not sure where the servo is or what it looks like, but if it's identical I see no reason to replace it unless mine turns out to be defective. I have pictures of both cars' engine compartments, just click link for the '78 in my signature, and here is the
'81 Mercedes 300D parts car.