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[NOTE I have this posted in heating/cooling as well..]

If you try to turn on the A/C from inside the car, the clutch on the compressor doesn't pull in (so no cold air blows, but the blower is working). If you jumper the pressure switch on the box on the firewall directly from the battery though, the compressor works (and cold air does begin to blow). I know there could be many, many reasons there isn't any power making it from the inside of car to outside, but I'm wondering if anyone knows of any very, very common places that could cause this (maybe I missed a ground inside, or something?). Thank you.
 

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I am assuming when you applied power to the thermal switch, you tried it on both sides. It should work on either side if the thermal switch is OK. Hate to miss the obvious. If you selected the lever switch over to A/C the compressor should come on. If not I’d look for power down on the blocking and anti-dieseling relays. See if you have power on any wire down there. Believe they are under the dash near the glovebox. Somebody correct me if I am wrong. These relays are unique to this car.
 

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When you say jumper does that mean you are jumpering the two wires together? I am going to assume this:
This means one of two things 1) Not enough freon in the system or low pressure. 2) Bad pressure switch.
I am also going to assume you don't have access to AC guages. Does your system have a sight glass on the dryer? If so jumper the switch and look at the sight glass for signs of air bubbles. If you see a lot of bubbles you are likely low on freon. If you see no bubbles and the AC vent temperature is ~45degrees (dependent on outside temp) you likely have a bad pressure switch.
DO NOT RUN THE SYSTEM WITHOUT THIS PRESSURE SWITCH FOR ANY LENGTH OF TIME.
 
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