Tried to find the thread I started with evaporator but couldn't. A/C repairs now complete and cooling.
I had concerns about the poa update not cooling. Complaints of cycling, not cooling. I went to Old Air Products. I was told the problem with the poa update using the pressure switch is caused by other issues in system. Clogged evap core, restricted condenser. That and freon level must be within I think he said 2 oz.. I was told the poa update using the thermal switch was more forgiving and has worked well for him over 10 years. That kit is expensive, but there is a way around that where it would be cheaper than the pressure switch kit. Buy just the thermal switch and gut your original poa valve. I bought the complete kit because if I wasn't happy with it I wanted to be able to have my valve rebuilt. If ever a next time I'll buy just the switch.
I removed the hood and removed condenser to flush, remove any debris between cond and radiator, and seal open areas between the two. I used a 2.25 x2.25 piece of foam from home depot across top and down right side. Worked like a champ. Ambient temp in shop was 110. Low side was 28. High side 150. Center vent temp. 58 degrees. This was on 3.25 lbs. of R12 as charged by my old Robinair 17700 machine. With hood back on and blocking half the condenser pressures didn't change, and using a large fan in front had no effect. Normally I wouldn't be happy with 58 degrees but considering ambient temp of 110 that's more than a 50 degree drop.
At 2,000 rpms it never cycled off, never froze up. Currently the hi speed is not working. All results are with blower on next lower setting. I had to remove part of dash to adjust blend door. It was open about an inch always adding hot air closed or not. Once I have it all back together and drive it I will update any changes.
One other thing, the aluminum A6 replacement compressor is quiet, has very low drag and weights 20 lbs less. I spent more than I planned, but usually do. Best price for compressor kit was Rock Auto. Old Air for evaporator, and they will sell just the thermal switch. Part # in pictures.

Thermal switch. Probe placed with expansion valve bulb and sealed with that black tar tape.

Old but still worked.

Was half blocked with trash. Has probably been leaking since the 70's.

110 ambient in shop temp. Idling, no aux fan. No change in pressures at 2,000 rpm's.

Seal used.

Center dash temp after 20 minutes. I expect lower temp with a more reasonable ambient temp. In shop temp actual increased to 120.

 

You may want to check the blower switch high speed relay. I've changed mine twice. 50deg drop is great. I hope I get that on my system. Switched to cross flow condesor and just got some brackets for a Sanden compressor. I just got tired of throwing money at the old system. Its been around 110-15deg here in AZ for a month and I dont have AC. I'll get it working good around Nov.

 

I didn't go with the Sanden because of the lower capacity. I've never heard anyone complain about it though. My original plan was to do this on the cheap. Replace evaporator core, dryer and clutch hub bearing. Flush pag oil and 134a. Recharge with 12. I should have stuck with my original plan. Instead I replaced compressor which lead to expansion valve and poa. The real key is get trash out of evap case.

 

Find your old thread. Hit search. Hit advanced search. Go to window top right sez username. Type in you. Then where it says posts, hit pull down and u will see threads started by user. Go to bottom hit the search now and you will find all threads you started. this one? https://www.corvetteforum.com/forums...vaporator.html or this one? https://www.corvetteforum.com/forums...-c-update.html

 

Thank you, you been most helpful since my arrival.