There used to be an "alternative refrigerants" bulletin board over at aircondition.com. Alternative should be read as "roll your own out of grill gas." There were many positive testimonials, so yes, hydrocarbon refrigerants work just fine. I understand hydrocarbons are quite commonly used in refrigerators and/or home air conditioners in Europe. About the only complaint I recall is that hydrocarbons don't perform quite as well as CFC/HFC/etc. refrigerants in extremely hot temperatures - think Phoenix.
I've been playing around with R406a in my 124 wagon. (Autofrost is the brand name - http://www.autofrost.com
) It's a mixture of R-22, R-142b, and about 4% butane (forget the R-number for butane). It has the same pressure/temperature curve as R-12, but is capable of carrying more BTUs. In 18 months it hasn't destroyed the system, in fact it works fabulously. I drove the wagon down to the the hill country last weekend, and the a/c produced 30F duct temperatures with no problem. (I modified the ETR to permit the evaporator to get colder before cycling off the compressor.) Shoot, the thing was too darn cold, believe it or not.
Biggest problem for R406a is that it's a bit hard on o-rings. You need to hunt down and replace everything with neoprene. It can be a bit of a chore. Being a blend, it also tends to fractionate as it leaks, but this seems to be a bigger problem in theory than in practice.
In general I agree with the ever eloquent Larry Bible - stick with R-12. However, my personal stockpile of R-12 ran out two years ago. I don't care to find brittle o-rings and leaky evaporator joints using R-12 at $22/lb. Check the pricing at http://www.refrigerantsales.com
- a cylinder of R-12 is $655, an equivalent cylinder of R-406a is $195. Wasn't a difficult choice for me to make.