[tjts1]

Duracool (propane/butane mix) works really well in an R134 system. The real plus side is that it functions at much lower peak pressure than R134. On a R134 car charged with duracool, the AC never triggers the high pressure switch which cycles the AC on and off. I simply keep it running for 1 minute until the vent temp drops below 30f (outside air temp in the 90s) then recirculate the cold air in the cabin for 5 minutes. 1 minute on, 5 off, repeat. R134 AC systems are over sized to make up for the inefficiency of the refrigerant. The lower pressure in the system will also reduce the load on the engine when the AC is engaged. Although duracool and R134 can mix, to do it legally you need to have the AC system vacuumed out of the R134. You don't need to torture yourself for FE.