Here is what I know. I like to play with the old style C-60 G.M. A/C units.
I get 38 degrees out of the center vent on my 1970 ( Fake / Fraud ) SS 454, 70 Nomad Sta. Wgn. First I wanted to keep it looking close to a stock 70 A/C unit.
I sent my P.O.A. to Florida and had it set for R-134.--- #2--- I replaced all the A/C hoses with ( look like O.E.M. BUT R-134 compatible ). ---#3--- R-134 compatible dryer. ---#4--- Find the largest Parallel flow condenser that will fit. I also have from the Fla. guys a modern 10 Cyl. R-134 compressor (painted black). Charge it with 80% of the Org. R-12 Charge. Why ,, So much changing of parts?
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HOSES-- R-134 Molecules are much smaller than the R-12 and will bleed through the Org. style hoses, And the front SEAL of the old style A-6 compressor, unless you can find a new R-134 front seal. ( using org. hoses, and the A-6 you may have to recharge every 1-2 years)
DRYER-- Needs a different medium for R-134.
P.O.A.-- R-134 operates at a different pressure than R-12.
CONDENSER-- R-134 operates Appx. 20 % hotter than R-12. Need more Sq. Inches of cooling area.
EVAPORATOR--Your call, WHY? Can you guess how many Cu. Ft. of ( Dirt, Bugs, animal droppings, leaves, Etc,Etc.) air has gone through this unit in 40-50 years.
All of the above will give you KOLD air. Option # 2 Change out your old C-60 unit for Modern style R-134 G.M. unit. They work very well.
Option # 3 THE BEST OPTION on the planet,,,,,,, BARR NONE.
Rebuild your stock C-60 and shoot it with, Old Style "" R-12 "".
The old C-60 rebuilt along with R-12 is the KATS AZZ. The statement you just read about R-12 is " FACT " not fiction, And can not be DENIED !...
P.S. My one owner 1970 LS-5/ M-22 El Camino uses R-12.
69-72 evaporator remove. Pull the engine side of the suitcase and it will come out. no need to remove the blower side of the suitcase. I just changed mine, Thanx John Souza, MD.