i have heard of the propane based refreigerant but never tried it, but i have converted a couple r-12 chevy compressors to R134a. orileys actually sells a conversion kit for the cheby. dont know about a toy though. but when it was converted it never blew cold enough. like the guy from houston said, it is a must, im about 2 hrs north of houston. but my 91 is blowing cold on the stock charge so im pretty happy about that.