R12 vs R134

[Steve Sherman]

Although it has been a year or two since I looked into this, I recall a
company that was selling an R12 compatible replacement.  It was a
mixture of propane and butane and some other unspecified gases.  There
were several supposed advantages over the 134.

First R134 is only 90% as efficient as R12.  OK if you design for it,
but when you convert an R12 you will loose cooling power (their mixture
was as or better than R12).  Second this replacement mixture is
compatible with R12 and its lubricants.  No need to flush a system and
replace all the oil.  Third R134 does cause cancer, probably not a major
concern but if gonna have a leak in your car...

This company was selling a car conversion kit.  As I recall they had to
stop selling it because their product was not EPA approved for cars (it
was approved for stationary refrig units).  Needless to say much less
money than R12, but a bit more than R134.

I did not follow up, because I was not willing to wait back then for
them to get approved.  Don't know if they are still around, but I would
try them first.  I found them on the net.

HTH