Dash air was originally r12 which I used until no longer available. then converted to R134. New problem as it kept losing R134. Was told this was due to molacule size and the hose in the Barth leaked it out thru the rubber. Finally last year tried propane. Works better and no longer loosing fluid.

R12 and R134 are indeed similar but not identical. Newer R134 systems are designed for higher pressures than the old R12 systems. The car companies had to use better hoses on the R134 systems to prevent the leakdown.

Had the companies used better hoses in the first place, leakdown with either type would not have been a problem. Same goes for exhaust systems. When they were steel they lasted a few years. When they finally switched to stainless for a few bucks more, they were lifetime systems. I had a 1994 Ford Ranger for 21 years, nothing but rubber hangers were ever replaced. Same for my beater 04 Chevy pickup. Original cats, pipes, and mufflers.

Remember Ziebart, etc for rust proofing? Now the companies put an effort into corrosion protection and the cars go 10 years instead of 3 or 4.

Pet peeve, but I have been long disappointed by US car companies. Their engineers have known for years how to build things right but the bean counters force them to build inferior products.

As for propane, it is cheap and it works very well in auto AC systems. My old Chevy cools like crazy with propane. Nobody uses it for OEM because, oh my God, it is flammable...

Gimme a break. My truck has about one pound of propane in it and 36 gallons of gasoline! Our RVs already have gallons of propane in their tanks, fuel as well. AC systems usually leak down slowly so accumulation of propane would be almost impossible. Even in a crash and dumping the whole system it is a pretty small amount.

Propane is environmentally pretty harmless, a minor component in natural gas. Seems compatible with most AC lubricants too. Like Gary, my experience with propane has been good.