I have a 1978 300CD. The heat/ac is not working. I live in the northeast and need heat to drive for the winter (not so worried about keeping warm, but need defroster for windshield). I tried running coolant from the head to the heater core, to the pump, just to try and blow constant hot air. But, I recently found out that Mercedes cooling systems work backwards? Does anyone know how this works or how I can bypass the servos and what-not to constantly run hot air? If anyone has any diagrams or anything that show how it works I'd appreciate it.

Thanks,
Jay

I just purchased the digital servo replacement for $650 from DieselGiant for my 77 300D, no heat/air. Looked for used servo could not find, so am trying this.
Good luck, there is a thread on this site that shows how to bypass the servo for constant hot water.
Ron Moore