A/C Compressor "Pop-off" valve and engine overheating...

[Z3DannO]

Good day! I recently had my 1990 300ZX (Z32 - non-turbo) begin to run very warm (up to approx. 95% of the gague). I then discovered that my 45 min drive home in the TX heat could be managed by using the A/C on the interstate (with no additional engine warming) and then truning it off on the side-roads. Interstate driving kept it from running hot and non-use of the A/C meant absolutely no additional warming at all.Then one day I was driving locally on slow roads with the A/C on knowing I wasn't going far enough to overheat the engine (but I was keeping a close watch on it). Shortly after returning to my car and pulling out onto a main road I hear a loud shoosh noise (similar to a pressure washer) and noticed a little mist from the front wheel well). The was the freon suddenly rushing out of the A/C. A mechanic determined it to be the end of the gold, hex-shaped "pop-off" vavle attached to the A/C Compressor manifold. This is a valve not attached to the hoses, but the metal manifold those hoses attach to which is then attached to the rear of the compressor. A nissan parts dealer said I can't just buy a new srew-on valve and am required to replace the entire compressor (which seems to work just fine).

My primary question is, is the compressor going bad and causing the car to overheat? Since there's no overheating AT ALL when the A/C was charged and running I wondered if there's a connection. The mechanic suggested the pop-off vavle "popped-off" because there was a pressure build-up. I want to just replace the valve but am wondering if the compressor casn cause engine overheating or must I expect it to be something else?

I've attached a photo showing the screw-on cap (valve) in reference.

Thanks!

[MaximA32]

The only thing I could think of is that the a/c compressor clutch is starting to seize up. Without having the car in front of me it's hard to diagnose.