R-12 was made illegal by congress when Dupont lost their international patent on it (and thus all the profits). So dupont cooked up R-134 (patented of course) which is about 100 times more toxic to the poor schmuck working on the system and congress obliged by making it a legal requirement. It doesn't have the heat rejection specs that R12 does, and it'll kill ya, what's not to like? BTW, back in the 80's in the Corps, we filled a/c on our 159 hp diesel HMMV's with propane and DAAMMMNN did they blow cold. When's the last time you crumpled your dashboard in a wreck? I never have...