A/C In my 85 GMC...HELP

[chargedstang89]

Hello all....I'm kinda new here, so any help would be great. The A/C system in my 85 sierra is complete trash. I want to replace it, but I cannot find the wiring that should go to the compressor. The guy I bought the truck from was a moron. The wires hooking the accumulator and evaporator are there. I traced them last night, and they go into a wiring harness type thing that runs across the back side of the firewall. It ends almost in the middle of the firewall, and there is a flat, kind of square plug at the end of those wires. I'm thinking that there should be a wire that plugs into that and then goes to the compressor, but I'm not sure. The Chilton's manual doesn't show anything about the A/C, so I'm at a loss. Can anyone help???? If anyone could post pics of the wires, that would be awesome. Thanks...Josh

[mnick]

If you go to your local library and get on the internet
they should have access to "motoralldata" or "mitchell on demand" both of these sites contain very accurate wiring diagrams for your truck. you'll need to surf through the site
to find them, but it's very easy.

[hawkeye1101]

There should be a wire( usually lt green) that comes from the A/C control in the cab, to the pressure switch on the accumulator. The other side of the pressure switch(usually dk green) goes to one terminal of the compressor clutch. The other side of the compressor plug is ground.
In other words the switch is in series with the compressor clutch coil. HTH.