Remember to add / drain all the oil through the crankcase bolt in the bottom of the V5 compressor. It was still a hold over from the days when compressors didn't have to inefficiently circulate all the oil like a 2 stroke. You can always add some for component replacements to an open system, but the V5 (and the old A6, as well as some other non GM designs) actually keep it primarily where it is needed.
Don't assume I know better! I have manifold gauges with the blue low pressure line going to the firewall. In theory the yellow refrigerant hose connects to the blue hose via the gauge manifold. I'm not sure what valve you are talking about. I did have AC turned on in the car, max fan I'm not sure.
I am going to grab a junkyard compressor and chuck it in. I actually bought one but grabbed it off another 3.1L GM car and the ports were in the wrong spot. So I'm going to exchange it today. Any advice on procedures is welcome. I've watched a few YouTube videos.
GM V5 is PAG 150 oil, IIRC. I even use genuine ACDelco refrigerant oil.
Note that some non-OEM compressors for GM applications may reference using a different viscosity oil, i.e. PAG 100 or PAG 46. If this is the case, follow that manufacturers recommendation.
Unless the compressor is physically in a position so that you can drain and refill the crankcase (the drain is always within about 20 degrees of pointing straight down on the V5, IIRC), you are faced with adding oil into the system like other sump-less designs. GM manuals have specs for this as well. The crankcase is under pressure when the system is charged, but there have been exceptions (non-GM) with isolation valves that did allow for compressor lubrication service without discharging the entire system.
The compressor you found definitely has a protective coating!
Success! Mostly. Here Adam is draining the oil while Matthew cleans up the rear cupholder. The anti-rattle foam had rotted.
In the name of science we took some stuff off the old compressor. Here is a valve thing:
Unfortunately they used sealer at some point. So the air is nice and cold. It was 48F out of the vent. Unfortunately my high pressure valve was leaking when I removed the manifold QD from the fitting. How well do those caps seal?
I busted the shaft of the old compressor trying to pull the clutch. Looks like there is a special slide hammer tool required. Is that right?
Also, I figured out why it was so hard to get the car to take refrigerant. If you back the can tap all the way out, the can seals up. I guess that is why they are called self sealing cans. The right thing to do was run it in, then unscrew it halfway or less.
IIRC, the W-bodies became known for evaporator leaks since they hung the evaporator on a string and built the car around it. Look for a glowing streak out of the drain. I hope for your sake it is only the high port. Even if the old story of the cap on the port being the primary seal, it is probably even less effective with the R134a style caps. I do put Nylog on the o-rings of the caps to try and reduce leaks.
The old 460 A/C was unpleasant even when I was young.