I will be ordering a case of this stuff called maxi frige this week, it runs $110 for 24 15oz cans. It is designed to be a direct drop in replacement for either system, no modification or oil change is necessary. According to their web site and flyer it is 60% colder than R134-A and a 50% lower head pressure than the 134. I should have an idea of how it works next week.

I converted my R-12 to 134-A in '98 using the conversion kit and a set of pressure gauges. The 134 runs at a higher operating pressure, so you can only run 80% of what you would with r-12, in an R-12 system. This higher pressure is hard on R-12 compressors after time. The one thing I noticed between the 2 is that the compressor runs constantly with 134, while it used to cycle on and opff with the r-12. The 134 also doesn't cool the vehicle off much. With the r-12 my truck would get down to 28 degrees at the vent, and the vehicle would cool off enough to have to turn the fan down. With the 134 it never gets cold enough to turn the fan down or off of recirc. The 134 might cool better in a lighter colored rig than in my black one. If I had to gauge the temp 134 cools down to I would say about 80 degrees in my truck, cooler than the 105 outside, but by no means chilly.