According to the paperwork sent with my order, Maxifrig is compatable w/both R-12 and R-135 oil, not sure about mixing the refrigerants. When I converted from r-12 to 134 I had a shop evac. the R-12, when replacing the R-134 I had a buddy's shop remove the r-134 refrigerant. The first place I went to said they wouldn't touch it because it was an R-12 system, something about contaminants from the R-12. If you want to try the Maxi-frig and don't want to buy a whole case, let me know, I have 16 cans left. I have convereted a couple more rigs this spring.

If the shop does evacuate the entire system, you can get a can of R-134 oil, you will also need to get the R-134 conversion nipples, and the hoses/gauges. You can't get the R-12 equipment anymore(atleast not here in CA) w/o a license, and the older style R-12 hoses don't fit the Maxi-frig cans. It might be cheaper to buy the R-134 conversion kit over buying the pieces individually.