It's been several years since I had to work on AC systems, and they were the old R-12 systems. However they did have oil charge bottles that went in just as if you were charging the system. I'm guessing they have similar for the current set up with R-134. I used to mix a substitute for the old R-12 using a mix of Propane and iso-butane instead of the R-12. Works very well, and if you research altenative to R-12, you'll find this info. I perfered a mix of 75% propane and 25% iso-butane (by weight).
Checksix
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