1971 c10 coverted to R134 pressures too high?

[bautino95]

Hi. I recently converted my AC to 134. Clean and flushed everything. Recalibrated my POA valve. And got a new compressor. Pulled vacuum and leak check held good. Started to charge system with 12oz. Cans of r134. Only got 2 full cans in and some of a 3rd can. I stopped charging the system because the pressures are too high. I was having about 35psi on the low side and 325psi on the high. It was about 90* outside and I had a fan blowing on the condenser and engine rpm about 1000 rpm. I cant remember off the top of my head but I think I added 3 oz of PAG oil to the system when I redid everything . I'm thinking I need a new thermostatic expansion valve or POA valve. Looking for advise on trouble shooting.
Thanks

[weq92f]

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This is a good read:

https://67-72chevytrucks.com/vboard/...d.php?t=822344


Hth,

-Kevin

[RustyPile]

Suction pressure looks about right. What's the dash outlet air temperature?? If the inside cab temperature is high, until the temperature is brought down, high side pressure will be elevated somewhat. When replacing R-12 with 134A, ounce for ounce, ~ 20% less 134A is required.. You're near the correct amount.. You might try an old timer's trick.. Spray a fine mist of water on the condenser and see if the high side pressure comes down..

[bautino95]

I ran it again for a little bit with out the gauges hooked up. Vent was blowing about 80*. I,m going to check pressures with a differant set of gauges to to verify my harbor frieght set is accurate. But can't do that till Monday.

[howzzzit]

You didn't say what compressor you used. Did you change any lines. Looks like you have a restriction in the high side. I'm still using the old style Frigidaire compressor on R12. It holds 3lb 4oz so if that's the compressor your using you should start at 41 ounces of R134 and go from there. If another compressor style I don't know. With that high of a discharge I'll bet on a restriction. I'm a 72 C10.

[bautino95]

Replace with a new A6 aluminum compressor. Replaced all lines with new. New dryer. Flushed evaporator and condenser. Recalibrated POA valve for r134. Have a little.more then 24 oz of refrigerant. Only things I reused was the POa, expansion valve, evaporator and condenser. Hoping the oil just needs to be distributed through the system and the pressures will come down. But I'm gonna try a differnat set of gauges to make sure.
Thanks for the help everyone.

[bautino95]

Well, no luck with the differant gauge set. Still getting too high of pressures. I'm going to evacuate the system and start with the expansion valve. I have an old AC repair book and it days there is a screen in there that is serviceable. Fingers crossed.

[weq92f]

Originally Posted by bautino95

Well, no luck with the differant gauge set. Still getting too high of pressures. I'm going to evacuate the system and start with the expansion valve. I have an old AC repair book and it days there is a screen in there that is serviceable. Fingers crossed.

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I'll concur, a plugged TXV can manifest as an overpressure. Didn't know they were serviceable though?

-Kevin

[bautino95]

Here a Pic.

[Steeveedee]

Friend @Richard here on the board pointed out to me that the factory R12 condenser isn't up to the job of cooling the high side when using R134. I'd check deeper before draining, evacuating and refilling your system.