I just finished installing a new compressor, receiver/dryer, and expansion valve. Hooked up vacuum pump and held at 29" for 30 minutes. Charged with two 12 oz. cans of R-12 to get started. First problem is the compressor clutch stays engaged all the time, even with the switch disconnected at the receiver/dryer. Second problem is I don't even get a hint of cool air at the vents. Also, the gauge readings are not even close to what they should be. The low pressure side is at 40 to 45 psi. The high side is very low ----- can't get it above 30 psi. This is a new compressor, not a rebuilt one. I followed the instructions carefully and added the correct amount of R-12 oil to the compressor amd receiver/dryer at installation. I am really puzzled by the extremely low pressure reading on the high side gauge.
One more thing ----- when I installed the new expansion valve, I just pushed the coiled probe into the opening at the evaporator. I don't know if its actually touching the inlet pipe. Could this be my problem?
Another item that I'm not sure of ---------- what is the device under the black cap at the receiver/dryer outlet tee? I removed the black cap and saw what appears to be some type of valve that goes down into the tee.