How to find a mechanic for R12 AC unit. (Page 2/2)
sanderson231 AUG 02, 06:49 PM
I would remove the compressor, evaporator and condenser and dump any oil in them. Flushing is not required. Add PAO-68 oil w/ UV dye to system as follows; compressor 2 oz, new accumulator 3.5 oz, evaporator 3 oz, and condenser 1 oz. Replace all o-rings with Buna-N or Viton. Lubricate o-rings with Mineral or PAO 68 oil. Pull vacuum on the system making sure it is an almost perfect vacuum i.e. -29.92 "Hg. Keep the vacuum pump running for at least one hour. This will get any moisture out of the system. Block off from pump and see if vacuum holds. I like to see no movement in the gauge after 1 hour. If it does not pass a vacuum test, charge enough Freon into the system to get at least 50 psig pressure. Soap test all the connections. Repair as necessary. When the system passes 1 hour vacuum test, charge Freon through low side port. I charge from a 30 lb cylinder and do not have a scale that can measure weight change. So I charge based on high side pressure based on chart in factory service manual for high side pressure versus ambient conditions. If using cans it takes about 3 14 oz cans.

Hope this helps.

p.s. PAG oil works well with R-134a on new systems. However it is not compatible with residual mineral oil from an R-12 system.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

sanderson231 AUG 03, 01:14 PM

quote
Originally posted by latyart:

R134 does run at higher pressures. Really is sub-par in a system designed for R12. The R12 systems don't have the necessary capacity to cool well with R134. (of course, I am in Texas )I have been through the A/C stuff with a '77 turbo Carrera (not enough capacity no matter what you do), '86 Carrera, 96 Carrera, 90 C2 & 91 C4. When it's 100+, it gets really tough to get the systems to recover after sitting in the heat. The 964 & 993 systems do surprisingly well with the capacity Porsche added to the vent system starting in '86. Give the Freeze 12 a shot. I oftenly read new articles on hvaclifehack.com, try to read them, I think you will be pleased.



Freeze-12 is 80% R-134a and 20% R-142b. If you put Freeze-12 in the system guaranteed no shop will work on your car. No experiences with Porsches but straight R-134a works well in Fieros. The difference in boiling point between R-12 and R-134a at typical low side pressures is only 3 'F. The high side pressures will run 20-30 psig higher with R-134a vs R-12 and that hurts the compressor capacity a little but not enough to matter.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged