Blue Angel

OK AC gurus, here's the deal… My '02Z AC isn't working at all. The system is charged, though the car is getting old and could be a bit low on refrigerant. There's enough refrigerant in the system that the low pressure switch is triggered and the compressor clutch engages when AC is summoned from the HVAC unit. All vacuum controls in the HVAC seem to operate properly.

I put a gauge on the low pressure fitting and checked the pressure with the AC compressor running. The gauge read 140 psi which, according to the markings on the gauge, is way too high. So I shut the AC compressor off and the pressure remained the same.

A little bit of research suggests that the compressor is a V7 model, which has seven cylinders and is a swash plate design (the swash plate angle is adjusted to vary the displacement of the pump). Since the low side pressure isn't changing with the compressor turning, the swash plate likely isn't moving and the compressor's displacement is effectively zero (not pumping at all).

QUESTION: Is the swash plate angle regulated mechanically (internally) by the compressor, or is it regulated by an external electrical signal? It's hard to see much from the top, but I could only see one electrical connector going into the compressor and as far as I know this is only for the clutch.

The AC worked flawlessly up until last fall when it sat unused for three weeks while I did a cam/lifter swap. The compressor was not touched during the procedure, but the AC didn't work when I fired the car up afterwards.

Quicksilver Vert 01

There is no external control of the swash plate, which regulates the compressor's effective displacement. The angle is controlled internally by the delta refrigerant pressure of the suction and discharge sides, of the A/C compressor, during it's operation.

During operation, higher suction pressure should result in greater compressor displacement, and the effective displacement gets reduced as the suction pressure lowers.

Blue Angel

Thanks man!

That's what I thought... so it would seem my swash plate regulator (or whatever it's called) is stuck in the "zero displacement" setting. Any idea if the internals of these compressors are serviceable?

If they are not, what would be suggested as a good replacement unit? Are there savings to be had by shopping outside of the GM Delco parts bin?

Quicksilver Vert 01

I wouldn't attempt to repair it, unless you're prepared to buy, beg, borrow, or steal all the special tools that are required.

There are savings to be found. Several years ago, I bought a brand new compressor for my old Silverado. It was a "private label" GM/Delphi clone built to the same OEM specs.

My son has that truck now, and the A/C is still blowing cold!