A/C compressor question.

87 Ramcharger, I converted my ac to 134a. Changed the expansion valve, filter drier and clutch. Pulled a vacuum and charged it with the conversion kit. At idle, the pressures are right, but as soon as you raise the rpms, pressure drops off. Doesn't really blow cold. At idle the suction line will sweat some at the txv. The compressor growls some and I think it is bad. Am I on track with that? I wanted to be certain before ordering another compressor.

I had the same thing on my 93 ram. It was a bad pump.

Are you looking at both head and suction pressures?? Which one drops off?

Sounds like a bad compressor.

Well, you could pull the discharge line and look for metal. Hard to diagnose a growl over the internet. What is the discharge pressure? You should have around 30 psi suction at 1800 rpm, you don't want it lower. Discharge varies a bit with the outdoor temp, 120 to 190 with low-medium load.

I put a rebuilt compressor in my 2002 T&C (Nippdenso, similar to Sanden). It made a slight growling sound and barely made it thru the rest of the summer. When worse the next May, I took it apart and found the rebuilders had put 2 flapper plates (stuck together) on one side and none on the other side. The backer plate had been serving as a poor flapper on that side (marks from ports). I reassembled it correctly and has worked fine since. I actually changed to the center section (swashplate & pistons) from my OE compressor since it had less play. The original problem was that the clutch spun and melted on a 108F day. Probably my fault since I has slightly overfilled the system. During above, I added a tiny pressure relief valve (~290 psi, $8 ebay) so it wouldn't stall the compressor again. No worries about venting since I use Duracool HC refrigerant, but don't suggest it for people who fear it coul "blow up" (many absurd claims). I did Phd research in combustion, so not an idiot.

Thanks, yes I only can check the suction with my gauge. I can't recall right now the pressures, but the higher the RPM, the less pressure. Actually drops rapidly, which makes me think the compressor is shot. I replaced the clutch at the end of last summer. It is the factory unit, so a new one is in order.
I will replace the drier, but should the txv be changed again too?
Thanks, Paul

It does sound like most likely a bad compressor. Be wary tho, that a restriction in the system will act in a similar fashion, and of course can fry a good compressor as well. You do need to change the drier, and the TXV should not need to be changed, but if there's a restriction, it is most likely right there at the TXV inlet side.
HTH, Lefty71

An AC guy will check in but, isn’t the pressure test off idle. I’ve always seen specs for pressure at 1200-1800 rpm.