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After several steps forward and many more backwards getting a low-pressure (LP) fitting to work on my 73 I was finally able to charge the AC system today for the second time with R134a.
Steps I performed in the vacuum / charging process
1) Pulled vacuum to -30.8 inHg for 1 hour
2) Waited 30 minutes and vacuum held at -30.8 inHg
3) Pulled vacuum to -30.8 inHg for 2 hours
4) Waited 19 hours and vacuum held at -29.8 inHg
5) Added 39 oz of R134a
Operational Check Ambiant Temp 85 degrees
1) Low Side is reading 65.7 PSI
2) High Side is reading 187 PSI
3) Air Temp in cabin at vent with blower on High is 70 plus degrees
4) Evaporator inlet and outlet are cold
5) Condenser inlet and outlet are warm
6) Compressor Low Side hose is cold
7) Compressor High Side hose is warm
It would appear I have a High Low Side / Low High Side condition. The compressor appears to be doing its job and the clutch switch and Superheat switch check good per GM testing procedures. Everything I have read on the subject points to the Valve-In-Receiver (VIR) being stuck closed or restricted. A stuck closed condition seems to cause warm Evaporator inlet and outlet which I don't have so maybe restricted.
In my internet travels I also came across talk about the GM VIR being non compatible with R134a, will it work yes but not very efficient in hot temp. My goal at this junction is to punt and bring this AC system back to OEM as delivered with a R12 charge but before I do that, I need to figure out this High Low Side / Low High Side condition. I'm not opposed to sending out the compressor and VIR for overhaul but would like to know what part in the system is causing this condition.
I will let others chime on vir..and pressures do seem high on low side.
But I think you have a leak still. If you redo i would pressure check it with air.
what kind of vent temps are you getting? Assume pretty high…60’s.?
Mr. D, I had a very nice '73 with A/C a couple of years ago. I'm in the California desert where triple digit temps are pretty common so it was imperative that the A/C system worked properly. Do yourself a favor and dump that VIR. It was poor design from GM and they knew it. It failed on every platform used. After 3 miserable years they dumped it. Install a VIR eliminator kit like this one: https://www.ebay.com/itm/19077376152...QAAMXQJzRQ031x I posted a follow along thread with pics when I did mine: https://www.corvetteforum.com/forums...liminator.html Install was easier than I thought it would be and the results were terrific. The change up is very clean when finished, and looks relatively stock, this is NOT a Frankenstein type mod. If you really want your A/C to work properly and blow cold in the highest ambient temps, I thoroughly recommend this change up. Cheers, Greg
and put a shut off valve on one or both heater hoses. if evap hoses are cold and air comes o0ut at 70 degrees your heater is beting your ac. if you insist on absolute stock you could remove a heater hose and thread or silicone a plug in intake fitting. but a valve lets you turn on defroster when needed and turn it back off later. but i agree with greg. that VIR is crap.
Ran the AC today on cold startup and the vent temp was 56 degrees and I agree the VIR and heater core are contributing factors to this. Looks like a winter project is in my future upgrading this AC system.
But it will take a half hour to shut off the hot water to that heater. And heater running is the biggest contributor to cabin heat. Even when there is no ac. Hell, especially when no ac…
Let talk 73 Air Conditioning System
