The AC on my 2008 Mazda3 fails to cool the car after I've been driving it for more than 10 minutes or so. It's able to produce cold air while I'm idling from a cold start, but it seems like the compressor refuses to turn back on once the car has been warmed up (even during a hot idle). If I let the car cool back down and start it up again, I can once again get cold air.
I already checked the pressure on the low refrigerant line using one of those refrigerant recharge kits with the built-in pressure gauge. When I can actually get the compressor running, it shows a normal refrigerant pressure. I do notice that when the compressor cycles off, or is refusing to run at all, the pressure gauge shoots up into the red "overcharged" zone. I did not add any additional refrigerant so I assume that this has something to do with the pressure feedback switches that internally control the pressure of the refrigerant. Am I correct in assuming that this is a normal behavior?
My next step (inspired by the Haynes manual) was to inspect the compressor belt and compressor clutch. I removed the front right wheel and the wheel well trim:
The belt looks fine and feels taut. I removed the clutch plate and inspected the inside surface:
Aha! The surface of the clutch plate appears to be heavily corroded. According to this source, this corrosion can cause the clutch plate to slip when it is supposed to be engaging the compressor pulley.
Is this the likely source of my problem? Why would it only be an issue when the car is hot (thermal expansion?) Can I just dremel off the rust or do I need to replace the entire clutch assembly?