The fresh/recirculated air doors and compressor switch are activated by vacuum. The vacuum is supplied by the engine. A vacuum tank is mounted to the driver's firewall under the fender. The tank is a vacuum reservoir and maintains a high vacuum level to operate the A/C system when the engine is under heavy load and engine vacuum drops. The larger vacuum port connects to the engine vacuum source. This port has a check valve so that the vacuum in the tank is maintained when the engine is off.
The vacuum tank outlet line goes through the firewall through a hole located just above the steering column. A hard plastic grommet protects the line where it goes through the firewall.
All of the factory documentation I have seen just describes the source vacuum line as connecting to the engine vacuum source with no other detail of exactly where the line connects. Mine was disconnected long ago, so I don't have a good reference here. I imagine the engine vacuum connection point is different depending on the engine/carburetor combination.
IF YOU CAN HELP - It would be nice if owners of A/C equipped cars could post what engine/carb combo they have and what is used as the engine vacuum source for the A/C system. (Thanks in advance!)
