Not sure what "compressor valve" actually is referring to. There is an electrically powered controlling valve within the compressor. It tells the compressor how much cooling air to output under varying conditions. That item is part of the compressor itself. Attached very near the compressor is the pressure sensor. Its job is to see if the pressure in the system is to high or to low. If it senses either one of those conditions, it will send back a specific voltage which would command the compressor (in essence) to shut itself down to save it. If you are talking pressure sensor, that ACDelco P/N is shown as # 13587668 or #15-51343 for about $28 on Amazon. Others that make that part, can be had for somewhat less. If its not that, you'll have to add some more info to figure out what's needed
Not the sensor, but the variable displacement control valve,does not look serviceable,but it is the culprit of many compressors replacements,found one on Amazon 30.00 as opposed to a 350.00 + comp. replacement
^^^^^ If your successful changing out that variable displacement control valve, an find that "it" corrected your problem, I hope that you will try to post up how you went about doing that. As well posting the P/N of that control valve, in case others have that feeling that doing the same, will correct their A/C as well.
It is a very simple procedure, once compressor is off you simply take valve out held in with a snap ring,push in new one and reinstall comp.vacuum and recharge,At GM i did many of them on later 4 cyl S10s,for opposite issue, The S10s would stay full flow freezing evaporator, The G8s sol. stays closed and a/c pressures never move after commanding on with tech 2. or 120 lbs low and high sides,of course the sol shows about 20 ohms but won't click when applied 12v, as it should click just as any sol. It is stuck closed I will post a complete swap when done, this is the link to valve,noting others will fit but connector ends are different...Go to Amazon and paste 1K0820803 6SEU12
look for the one with the pigtail harness as it is the only one that fits the G8 connector wires