Truck A/C compressor lifting relief valve

[xavier296]

I'm close to finishing putting an 05 5.3 engine in my wife's 89 Grand Wagoneer, and have the original AC system hooked up to the stock truck denso compressor. It is not a variable rate compressor (from many hours of google searches), so it should work. I have it wired through the jeep wiring running through the jeep pressure switch. The jeep had AC before, and it worked well with the installed Sanden compressor. So, I vacuumed it overnight, sat at 29+ vacuum for 5 hrs afterwards, then charged it. It blew cold and everything seemed fine until the lowside pressure (with charging valve closed) reached about 10 psi. The compressor started sounding like it is opening a relief valve. When you try to keep charging it, it just keeps opening the relief valve (haven't watched it lift, but that is what it sounds like). It does not blow cold like it is, but the clutch is engaged and the compressor is spinning.



Do I have a bad 100k mile denso compressor, or is it something else? Compressor is a 10s17F with a two wire hook up. Thoughts are helpful. I want to avoid buying another ac compressor setup that costs half of what the whole drivetrain cost but also don't want to buy a new truck compressor just to see it do the same thing.

[MonzaRacer]

Either you have it hooked up backwards OR a possibly a stuck expansion valve?
Or something stopped up?