I use Duracool. Propane/butane mix and lube. Works better than R12 or R134a, cheaper, less leakage, less pressure. Yes, propane will burn, but guess what? So will the other stuff.
We used to do a purge with propane. No vacuuming, just open a line and flow the gas in until it comes out the other fitting, and close it up. Pressurize, and away it goes.
Also uses half the gas that the R's do. I've been told the molecules are bigger so they don't leak as easy. ? Who knows?