First you need to find out which refridgerant it's supposed to use. When the industry began it's conversion to R134A in all the training classes I attended it was preached that you do not mix R12 & R134A ever!! The compressor oil's, hoses and just about everything that was not metal was not compatible. So my suggestion is that when you tear down the system you need to do a complete system flush. Then you can do one of two thing's. First you can go back with R12 if that is was originally used or you can convert to R134A, which could possibly reguire some hose changes and oring replacement. Either way you should not have both in your system.

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Keith Schuster
83 300D
auto\hydraulic mechanic 20 yrs