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isn't the temperature door,cable operated? the vacuum controls the mode,direction of the air flow. the system could be undercharged or overcharged. (ambient temp will cause this to do different things)The system should also shut off too prevent freeze-up. There would be a switch on the carb if it is equipped with a.c. throttle cut out switch.or could have a switch inline with a vacuum line.



I am not sure about the 73 E-bodies but the 71-74 B-bodies, all the doors inside the HVAC box are vacuum actuated. The only thing that is cable operated on the 73/74 B-body is the heater valve inside the engine compartment. Earlier years are vacuum here as well.

If he is running the original compressor, they had a valve (big honken canister looking thing) on the AC lines that would serve the purpose of not allowing the evaporator to freeze up. If you go to a Sanden compressor, you will need a separate thermal switch to do this.

With a factory 73 B-body setup, the only thing (besides turning it off) that can cycle the compressor is the low pressure switch on the drier. If you look at the wiring diagram, the AC compressor circuit comes from the HVAC controls to the low pressure switch then directly to the compressor. There is no connection whatsoever to the accel linkage or carb. I can't imagine the E-body would be any different.

Trace that blue compressor wire....I bet you will see it goes to the low pressure switch on the drier and then goes with the engine harness back to the firewall bulkhead connector. From there, it's straight to the HVAC head unit. Not anything else that should break this circuit....

Also FWIW, 73 B-body didn't get any vacuum canister I'm aware of. I know mine never had one. Maybe somebody can chime in but I am thinking the E-body would be pretty much the same. These engines from the factory pulled plenty of vacuum on their own in 73...