Does the fan run on all speeds?
Does the heater work when turned to heat?
Vacuum doesn't control the compressor kicking in...that's all electrical.
Check the ground wire(black) coming off of the compressor plug, and make sure it is connected tightly to ground. Check for 12v at the green wire on the plug(key on, A/C & fan on max). No voltage means either the high pressure switch(in the small A/C metal line) is bad, or the low pressure switch(usually mounted on the accumulator/dryer) is bad, there is no refrigerant in the system, the fan switch is bad, or the compressor "on" switch in the control panel is bad. By "bad", I also mean it could just be a loose connection.
Try jumping across the terminals of the pressure switches to see if the compressor will kick in. If it kicks in when you jump the low pressure switch, check the refrigerant pressure before going any further.
btw...the '77 could have either type of A/C system: The older style VIR set-up with the A6 compressor, or the newer style, with the orifice, accumulator/dryer system with the smaller, R4 compressor. Which does yours have?
Adams' Apple2007-06-20 10:04:46______________
Joel Adams
C3VR Lifetime Member #56
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