| PAG is not compatible with mineral oil and any residual R-12, only use POE. The existing oil doesn't magically find a place to hide. You need to remove as much of the old oil as possible, otherwise you have twice the recommended oil in your system, which can lead to reduced performance, or worst case oil slugging the compressor (essentially hydrolocking it). I have seen this happen first hand. Absolutely need to change out the drier to one that is compatible with R-134a. R134a has been known to dissolve the dessicant bag inside non-compatible driers, sending a gritty mess to the compressor. a high pressure cutoff switch is highly recommended, otherwise you can easily blow your high pressure relief valve.
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