need a lesson in A/C

I have 3-4 cans of R-12. But it's really not that hard to change to R134A. On my 69 Dart I flush the system with denatured alcohol. Installed a new dryer, drain my RV-2 compressor as best I could. Then I added 10 oz. of Ester oil which is the best oil to use when converting from R12 to R 134A, it mixes with any mineral oil that may be left in the system. Use a system vac pump to make sure it will hold a vacuum for 30 minutes. My Dart held 36oz. of R-12. When you use R 134A you use 80% of the R-12 amount, or in my case I charged it with 28 oz. It blows 36 degrees and the pressures were real good 35/225.