If you can keep the system on R12 then there is no need to convert to R134A. The system was originally designed for R12 and will yield better performance as opposed to R134A. Most people are not satisfied with the results of a conversion, even one that was done correctly. These cars just don't convert well.

As far as the compressor is concerned, you may be better off obtaining a quality rebuilt depending on how many miles your current one has logged. They do wear out eventually.

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1989 300CE