I have a 79 450 SL (grey). there are two problems with the climate control system that seem related but I can not find the common thread:
1. The AC does not work from the control panel "normally". If I "hotwire" 12 volts to the compressor clutch the AC works but the compressor remains engaged until I disconnect it from the "hotwire".
2. The heater does not work until I disable the vacume to the hot water input valve (located at right rear/top of engine) that allows water to the heater core. Then everything works at the control panel.
Both problems seem to stem from some control related problem.
I'm stumped, any help/suggestions would be appreciated. I live over 100 miles from the nearest mecedes dealer/garage.