Ooops! My bad! Thanks.
Yeah, thatās why the static pressures seemed normal to me. I figured it is pretty much filled proper amount but considering the alternative, dumping a small amount more in there to hopefully keep it off the floor may keep it limping along. I lean more and more toward the doomsday scenario thinking about how it performed in the testing above. But maybe I can eek one more summer out of it- Iām probably not that lucky but worth at least a shotā¦
The static pressure at ambient temperature tells you if the system has enough refrigerant.
Tester
It seems clear that something weird is going on inside of the system re: those pressures, but Iām not the right guy to ask about that.
But Iāll also tell you my āstoryā about my '02 Envoy which should be pretty much identical. Even if itās not part of the issue now, thereās a good chance it will be at some point - and maybe soon. A couple of summers ago on hot road trips Iād get in the truck and the A/C would be great. Then it would just randomly die and start blowing ambient. Sometimes it would kick back in. But often not until things cooled down again.
Anywayā¦it turns out that it was the clutch which worked when cool, but not so much hot. I measured the air gap and it was right at the outside of the range. (I forget the specs, sorry). Unfortunately, the last I knew you couldnāt buy a new clutch only - had to get the whole compressor. Ugh. I pulled the clutch, pulled the shim washers and then fashioned a washer that put the air gap at the low end of spec. Itās been flawless ever since.
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Before I did any diagnostics or took any pressure data, one of the thoughts I had was along the same line regarding the clutch. They wear and the gap gets larger. I am also familiar with inductive coils like this developing susceptibility to heat soak. I held a screwdriver near the coil when it was working and then not. It was clear that when it was working, there was magnetism and that went away when the clutch stopped. I even tried nudging it with a stick to see if it was marginal but that was a big nopeā¦
Unfortunately, I found out shortly after that the low pressure switch was activating (thatās another common failure in these) and then measuring the pressures and watching the gauge match the switch activation, I knew it wasnāt the coil, clutch, switch or the HVAC controllerā¦that seemed to leave- low refrigerant level, partially obstructed orifice, dirty evaporator or weak compressor. The potential for the dessicant bag being a problem didnāt occur to me until Dave pointed that out. The static pressure seemed very much in-line with the pressure charts I had so my hopes of a low charge were on life support. Thatās when I figured Iād seek input from the more experienced members here and am very thankful for all of your contributions to this discussion!!
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Oh, forgot to mention- early on I was looking around to see if I could buy just the clutch and I did find one place that sells a replacement clutch kit. I never went so far as to see if I could actually gain enough access to the compressor to replace just the clutch but watched some Youtubes of guys doing just that on other cars. That would have been a nice option 
with only 158k on the clock, I was hopeful the compressor itself wasnāt failingā¦
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Do you think you know what the problem w/your carās AC is now?
On a recent Best of Car Talk podcast Ray says heās having trouble with his home fridge. He phoned GE, who came a did a service, but it still wasnāt working. Maybe refrigerating systems are just meant to be frustrating! ā¦ lol ā¦
First, my gut tells me that Tester is right about the orifice, butā¦
Iām betting that you have a set of feeler gauges, and itās pretty easy to get those down there. I think the spec is .02-.03" or something. Mine was a bit over .03. The magnet might be energized, but if that gap is too big, it wonāt be a strong enough field to pull it in. Itād take you like 5 mins, so Iād at least check it.
This going back a couple of years now, so my memory is fuzzy on itā¦ And everything I am saying rests on the assumption that things didnāt change from '02 (my 4.2L Envoy) to '08 (your 4.2L TB). But I found one and only one. And it had to ship from China, and I think through Ali Baba or something. And the wiring had to be monkeyed with - not in any big way, but itās not plug n play. And itās really tight to work on and not so easy. Things might have changed by now. Iāll look again if needed.
Again, assuming the same set up (in which case the compressor is way down low on the left side of the engine under the left of the fan) - itās very tight down there and not easy. But I managed to finagle a 3/8" air ratchet down there which buzzed the nut off. I donāt recall the electrical connector, but I managed it with no bad memories, so it is do-able.
Not yet but I will certainly post back when I do. Unfortunately, I have an issue with my foot where I canāt stand or put any pressure on it. Hoping to be back on my feet (literally) in a few days.
Two years ago now, it was early November IIRC and I noticed one of the central air systems for my house running at less than 1/2 speed. It was cold enough for the furnace so that was odd. I flipped the outside cutoff and waited for some warmer weather to check it out. No signal from thermostat, fan running at 1/2 speed, compressor motor doing same. After checking the start/run cap and relay, I measured the motor windings and it fit all the tell tale signs of a compressor motor that was in black death mode. Closed it back up and waited for spring. Spring came and started looking around for someone to replace the system. Then I got curious and went back to re-measure the motor windings. Strangely, they were different. So I took more of the cabinetry apart to get better access. Thatās when I found a mouse had chewed through the wiring and made a nest. Two years now (knock on wood) itās still running. Ran for 36 hours almost straight the other dayā¦Sometimes, things have a happy ending
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It was fairly obvious with the screwdriver between when the coil was energized and the clutch pulled in versus when it wasnāt running. Itās a pretty easy and down and dirty check. At the back of the coil by the connector, the field is pretty strong and you can easily feel the screwdriver drawn in versus when the coil is not energized. Plus, if you recall, I said I manually pushed the clutch plate in with a stick and it still didnāt engage. That was just a what the heck, why not try and see if the air gap is too big or the coil is weak. I didnāt even bother hooking up a meter at that point. When I did measure the low pressure switch with my meter, it was easy to see it activate electrically so I knew that was responsible for turning off the compressor clutch.
I like that- with no bad memories!
Pretty sure this is the one I ran across:
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The low pressure switch turns voltage off to the compressor clutch if the pressure drops too low to prevent damage to the compressor.
But I think in your case, itās too late.
Tester