aidandrake

So, I've recently bought a 1976 Mercedes 300d (W115) and it's been a bit of a fixer upper, but it's a hell of a fun car. What I'm working on right now is attempting to fix the ac system, or at least trying to figure out whats wrong with it. I've manually hooked up the blower motor, and compressor to a power supply, to see if they both work and they do. So, I know the two main components work, but when I turn the knob for the ac system, nothing happens. The blower motor doesn't kick in, nor does the ac compressor clutch. So, I'm stuck. Is there anything I should be looking out for? Is there a AC system relay switch somewhere? Any help would be greatly appreciated!

tommd1977

Hi! If you have not resolved this, a few suggestions. The A/C knob has both and electric thermostat switch to control the temperature and a vacuum switch. When you turn it on, the vacuum switch directs vacuum to move a vacuum dashpot that moves the air direction damper and when doing so, it also trips a changeover switch. This switch changes the wiring so the fan knob now controls the A/C blower fan and turns on the compressor if the thermostat is calling for cool. First thing to check is if the vacuum system is working and moving the damper and tripping the changeover switch.
Tom