Hi
I am trying to fix my father-in-laws A/C on he's euro 1984 300D, The system is after market,i guess it was added when brought to the USA. I have resealed the system and charged it. It holds good. it was originally a R-12 but the PO changed it to R-134a.The problem is it sucks. it hardly cools, the expansion valve (also changed) does not even get cold.I know R134a is not as good as R-12,but compared to my 79 300D(R134a) he's car is sad. My question is would a new compressor help?.A Sanden SD508 is what he has,looks like its been on the car since the installation. The low side pressure is about 50-60 psi to get any cooling, the high side is not much more than that(what should it be).
I am also going to stick with R-134a R12 is just too expensive.
Thanks in advance.

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1979 300D.