Automotive Air Conditioning Information Forum (Archives)

ferricsteed on Tue July 05, 2011 10:42 AM

Year: 1971
Make: Pontiac
Model: Lemans
Engine Size: 350
Refrigerant Type: R-134A
Ambient Temp: 95F
Pressure Low: 32 psig
Pressure High: 250 psig
Country of Origin: United States

A few questions: Converted to R-134A couple years ago on 71 Lemans 350 lo-po. Not willing to stay with mediocre A/C performance any longer. Can I or how do I lower the factory POA setting down to 26 psig or at least to a lower setting? Still has A6 Harrison compressor. 3 lbs refrigerant charged. Is it worth switching to a POA swap to CCOT and of course what OT size if recommended? Coils cleaned inside and out by flushing. Original coils in place. The best air vent temperature is 60F, climbs to 65 at idle. Head pressure will build to 275 psig. (It is hot and humid in Louisiana). Low side at speed is 32 psig, tends to increase at idle speed to 37 psig. I replaced the thremostatic fan on radiator but didn't really improve matters. Yes, I will entertain recommendations on electric fans, different condenser if necessary etc. but naturally I try to keep at least close to stock apperance. I really want to get air vent temperature back down to a sharp cold mid forty's temperature. Thanks, ferricsteed

JJM on Wed July 06, 2011 12:45 AM

If you really want cold air, best bet is to stick with R-12. That will also keep it stock, especially if your concerned with points.

If you want to go with R-134a, you likely will need the largest parallel flow condenser you can fit in there. You will also need to adjust the POA valve down for R-134a from 28.5 PSI to 26 or even 25 PSI. Doug has an excellent piece on how to do this.

http://www.autoacforum.com/messageview.cfm?catid=20&threadid=16311&FTVAR_MSGDBTABLE=

Switching to CCOT and eliminating the POA ensures even more sub-par performance. Anyone who tells you to eliminate the POA is a hack.

You're also probably undercharged too. Original factory R-12 charge was 4 1/8 pounds, you're only at 3 pounds of R-134a - about 75% of the R-12 charge. Have you tried going beyond 3 lbs? Yes, high side pressures will increase, but if cooling performance improves, that will only confirm inadequate condenser capacity.

Joe

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