Trying to figure out AC

[Scratcher]

The ‘79 C10 I bought looks to be a non AC truck. Someone put an AC compressor mounted with what appears to be a fabricated bracket. There is also a condensor installed and an evaporator under the dash and the lines. I don’t know if any electrics are hooked up or even there. How do I figure out what’s been installed and what’s needed to complete the AC system?

 

[75gmck25]

Start out by putting gauges on it to determine if there is any charge in it. The hose fittings are different for the original R12 vs. the R134a conversion. Look for a sticker in the compressor or other components to see if it shows the refrigerant type and amount.

I only know how the original GM system was setup, but the add- on is probably similar. If you are lucky it might be Vintage Air, which is in San Antonio.

Most are cycling clutch orifice tube (CCOT) systems. The orifice tube is what manages the pressure difference that gives you the cooling, and the system just cycles the compressor clutch off and on to cool. There are low pressure and high pressure cutoffs to protect the system, and on the GM unit there is a low temp cutoff to prevent freezing. The original GM system blends cooled and heater plenum air to set the temp, but I don’t know how they do it in an aftermarket system.