[Joshua Paul]

Need some "expert" help or at least some Dad advice on my AC conversion from R12 to R134. It's been a couple of years of progress due to not being happy with the vent temperature or gauge readings. I am basing the gauge readings to modern temperature pressure charts found on the internet for a R134 system. Here is my current setup.

1. Recalibrated POA valve. Original recalibrated at Classic Auto Air in Tampa.
2. Parallel flow condenser from Classic Auto Air.
3. Hayden fan clutch and original fan. I do not recall if it was the heavy duty or the super duty.
4. New thermal expansion valve. I was not happy with the low side pressure and replaced on the last flush and recharge.
5. 190 thermostat.
6. New A6 compressor.

When I first converted, I was never really happy as compared to the temperatures of the original systems. I grew up in a gas station and remember how they originally performed with R12. My vent temp would only got to 50 on a mid 90 degree Florida day. I could not get the gauge pressure to be where it should be according to the charts Barely 30 psi on the low side and significantly over on the high side as compared to the charts. I decided to flush the system and replace the expansion valve. At current, the high side is where it should be but low side barely gets over 20 psi. TXV is supposed to be for R12 or R134. Current problems.

A. Low pressure does not go above 20 psi while high side pressure is where it should be for the temperature and pressure.
B. I suspect the evaporator is freezing up as it does not drip until I turn the AC off.
C. Vent temperature is at 40. Where I like it!!
D. Unsure of current charge pounds. I goofed and left a fitting not even finger tight when charging. It held a vacuum and charged well, but blew out a bunch of freon and exposed my error when I revved the motor. It took a few minutes to find my wrenches again.
E. High pressure line out of the compressor is HOT like it should be. Exit from the condenser is "ambient" temperature". My father the mechanic from 1968 to 1992 thinks possibly a blockage at condenser based on exit line temperature. I question do to a condenser he is not familiar with and the upgraded fan clutch.

So am I being greedy or am I missing something?

[Pete67FB400]

Have you seen this thread? It might give you some pointers or data points for what to expect from your system.

http://forums.maxperformanceinc.com/...d.php?t=809229

[bhill86]

Man, that’s a good write up. I don’t have an answer for you but I will be following this thread as I just installed the same system in my 77 T/A and I’m not 100% pleased with the vent temps I get. Around 50° at idle and maybe down to 40° cruising. I think there is room for improvement.

[padgett]

My 134 cars want about 35-40 psi on the low side running and I use a 180f thermostat on computer cars and 160f on non. What is your high side reading ?

[Joshua Paul]

Thank you for the link to the article. Found a few things to try.
1. Get some temperature points on the condenser.
2. Check the gauges and temps at 1500 RPM. All of my readings were done at idle.

Last time a played a few weeks ago, ambient was around 80. High side at 200 psi and low side around 20 psi. Still a bit stumped. Any advice is appreciated.

[Joshua Paul]

I did some reading on the four seasons website. When I filled the compressor with pag oil, I used all I had and was a bit short. The parts store was out of the small bottle and I used a partial can of oil while charging the system due to a knock in the compressor. Would to much oil cause a pooling effect in the parallel flow condenser and cause my low pressure side to read low. Can the condenser be flushed or does it need to be pulled out and tipped to drain?

[Formulabruce]

You probably know that R12 oil is different than 134A... Just making sure..
too much can cause issues with low side.

[Joshua Paul]

After lots of searching, I finally found the answer to my problem. I hope that this helps others when converting to R134 and have recalibrated their POA valve. The system now works like a champ!!!

I found this information on Original Air's website and it aligns with my system. https://www.originalair.com/about-poa-valves

Short of it is, a recalibrated POA valve for R134 is supposed to have a low pressure gauge reading of around 20 psi. High side will vary depending on humidity and temperature. In my case, I just needed to adjust the freon ammount in relation to the desired high side psi per the temperature at the time of adjustment. The system blows mid 40's out the center vent now.


134a
High Side Readings (Fahrenheit) Outside Air (Ambient) Temperature
115-200 70-80
140-235 80-90
165-270 90-100
210-310 100-110
R12
High Side Readings (Fahrenheit) Outside Air (Ambient) Temperature
130-160 60
140-170 65
150-180 70
160-190 75
170-210 80
180-220 85
190-230 90
205-250 95
220-270 100
240-290 105
260-310 110
285-335 115
310-370 120

[Formulabruce]

Excellent post and info, thanks for your work, Im sure it will help !

[gpmodelj70]

Just put R12 back in it...easy to get and not too expensive.

[77 Canamman]

Originally Posted by gpmodelj70

Just put R12 back in it...easy to get and not too expensive.

x10000