Thank,s Griff, I was able to do the first 3 so far. Here are results;
1. 59 microns
2. 290 microns and gauge was dead in middle between 25-30 so 27.5.
3. 270 microns
4. Will try to get tomorrow

I would make sure that the condenser is not dirty and plugged, so that your removing the heat, and getting a full column of liquid back to the expansion valve before it enters the evaporator. there is so much to this refrigeration stuff.

Thanks for the suggestion, the condenser has been removed, cleaned up and reoriented Last summer based on Griff’s guidance. Unfortunately the results were the same. As far as Ganum's suggestion regarding the expansion valve, I have wondered that as well but the symptoms seem to indicate ambient air in the system. I'm quite willing to replace the TXV at this point since I cannot imagine how I've gotten air in the system after doing this carefully so many times over the years.

If you go and do that, then while the valve is out disconnect the lines at the comp and flush the lines out with freon. Helps get air out and verify there is flow.

I have practically never seen a new expansion valve fail straight out of the box .. I have had to adjust a few, when they weren’t feeding properly, but that is rare also. What does your evaporator look like when you think your fully charged . Also make sure and purge your refrigerant line, before adding liquid refrigerant after a good vacuum below perhaps 400 microns .. if your not purging refrigerant line before adding refrigerant, you will introduce moisture. You might want to triple evacuate with nitrogen .. I realize you may not have nitrogen .. but that would be the best action . Do these systems have a receiver and a sight glass ..

Yea, when I recharge my 911 I do the belts, suspenders, staples and glue total overkill to be 100% certain there is zero moisture in there. I have a four valve manifold gauge set. Obvious high and low connection, one to the vacuum pump, one to the refrigerant tank or nitrogen tank. All lines are purged or vacuumed.

I start with a two hour vacuum pump run, shut it off, and let is sit overnight. Next day is pressurize with dry nitrogen (instead of the refrigerant tank) to 200 PSI, and check for bubbles in the connections using soapy water. Pull a two hour vacuum, pressurize with nitrogen to 200 psi. Leave that overnight. Check to see the pressure is the same. Vacuum again.

Then I change the oil in my vacuum pump, pressurize with nitrogen, then vacuum one last time down to the 300 microns if possible, then fill slowly with gas refrigerant. until it stops going up in pressure. Then I start the car, and pressurize to the proper pressures with a pressure chart and ambient air temps. I have four condensers, and all new hoses and the Griffith's evaporator. I really have no clue how much to add by weight. I get the pressures to my optimum numbers. Unhook, and go for drive.

Ahhh COLD air.

If you look around on YouTube you can see a guy use a bell jar to put water in a little container, pull a vacuum and most of the water boils off, but there is a large hunk of ice left. It sits in there for a long time before it sublimates, and puts moisture in the system. I am just paranoid that with the miles of rubber hoses ice is lurking. I kill it dead with my overkill system. A nitrogen regulator and rented tank of nitrogen is not very expensive, and beats wondering if there is moisture left behind.

One simple question ... is there a sight glass and a receiver on these systems .. I have an 82 sc.. and I can see the sight glass on my driver side fender ..

Glen you may be right. I vacuumed this thing down, let it sit for hours/days, vacuumed again and again. No leaks that I can find and could regularly get to low 300 micron range. It seems odd that there would STILL be water or ambient air in the system after all that, but what do I know. What's strange is it seems that several owners have been able to successfully recharge their systems without going to extremes as far as the evacuation process. I don't want to rehash things but I also had a setup where I could vacuum all hoses between cans and got same result. Finally, I highly regarded AC shop here in Dallas did a vacuum and recharge with the identical results as me. I still need to get Griff #4 on the list and will do that after work.

There is a sight glass, it is not easy to see. It is on the receiver dryer, and often rotated back against the body. Mine had a plastic cap on it to cover it. It is really not that useful of a tool on the 911. The pressures or the weight of the refrigerant is a much better way to charge it.

On my car I have to loosen the clamps that hold the receiver dryer in place, and physically rotate the unit. And remove the front tire to get my head in there to see the sight glass. And all I see is liquid and some bubbles flowing through.

I don't know if you got to watch the shop do the AC work. Even long time pros just can't grasp how many feet of rubber hoses there are. One of my friends is a pro that works at the local dealer. He helped me do it the first time. He though I was nuts to go through my many steps. But he is paid by the job, and speed is most important. Three days to do a recharge is just a possibility in the real world or professionals.

I don't think its a leak.... there is so much to check. I am a refrigeration mechanic by trade and have been working with all types of systems for over 20 years . you could have a bad compressor , who knows. you need a full system check. There is ways to check all of this? there is a lot of wrong information out there? anyways good luck!

Just quick overview, compressor is new and problem is same before and after new compressor. AC was decent before but decided to go full R134 conversion and has been PITA ever since. All parts brand new, hoses, evaporator, R/D, compressor, extra condenser with fan, all connections. Decklid and front condenser are only original parts and were flushed and dried thoroughly.

It does make me wonder if one of the hoses is pinched or restricted somehow. The route from front to back does go through some tight places.

Anything is possible.... but a restriction or a pinched hose would create no suction pressure and you would run in a vacuum .. he has suction pressure ..

Ok great so it sounds like it’s a refrigeration issue and not a part that is potentially defective , I wouldn’t change anymore parts until it’s fully confirmed that it is a defective part .. there is some things I have in mind to check.. but not sure if it’s possible to advise here ? ✌️

Was the liquid line filter drier changed

What do the vent temps get to when you drive it? What about at 2,000 RPM?

1) Wow, that is a good pump. By the way, what is your altitude above sea level?

2) Hhmmm, well 290 microns equals 29.91 inches of mercury.

Are you using any hoses that have one way check valves ?

Yes it will be interesting to read what item "4" above is.

Sorry for delay, have part 4 data.
when the gauge is at rest "zero" it is on about plus 2 1/2 lbs, maybe a TINY amount less. After running for about 30 minutes it is just shy of dead in the middle of the 24 and 25 lb hashmarks. If I let it run 3-4 hours is is perfectly centered between 24 and 25 (24.5 lbs) and never goes further regardless of how long it's run. It will hold that for hours.
Regarding other questions the r/d has been changed and the vent temps in prior vacuum recharge attempts it never got below the upper 50's then would climd to low 60s. Out of curiosity I ran it after only putting 1 can in and am getting mid 70s at upper 90's ambient. Core temps always a couple degrees cooler, which makes sense. I noted the pressures when I ran it the other day and was as follows
30 seconds 12/130
60 seconds 15/148
90 seconds 20/150
2 mins 20/150
3 mins 22.5/175
4 mins 22.5/180
5 mins 24.5/190
6 mins. 26/200
note that this was with 1 12oz can in the system. I have not added any more R134 yet.

I think next step is to add 2nd can of R134 to see what happens. Was just curious to see if any of the above results indicate ambient air ALREADY in system, in spite of what appears to be very well vacuumed system and careful recharge process. If this fails...again...will try a new TXV. They are not expensive and maybe I'll see something when doing that work that will indicate what's wrong.

OK...didn't want to start ANOTHER "my ac sucks" thread. Some have said its helpful (critical?) to purge ac system with nitrogen so I went out and got a tank and regulator. Only problem is I can't find detailed instructions on how to do it. I have a pretty good idea but wanted to make sure I was on the right track. I found this video and it seems pretty straightforward https://www.youtube.com/watch?v=E_UF7XtW8qI. He's got a very high end 4 hose gauge so I'm going to just use two hoses with shut off valves on the yellow/common line. I like this since its moving through the system as opposed to just emptying into the vacuum. Hopefully this addresses my ongoing issue...just in time for fall weather...