I can't compare a serpentine condenser to a parallel flow condenser but I can compare R12 to R134A with a PFC. I installed a PFC on my SD. I started with r134a in it and I wasn't too happy with the temps so I switched it to R12. The vents temps were only marginally better with r12. Something like a degree or two difference.

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD