been thinking about converting over to freeze 12. any opions on this stuff? does it get as cold as r12? any special things i need to convert it over? also, i have to replace my compressor and i found a used one for a decent price. is there any way of telling if the compressor is any good before buying it?

 

freeze 12 is mostly (>70%) 1,1,1,2 tetrafluoroethane (according to their manufacturer safety data sheet [msds] available here: http://www.freeze12.com/pdf/6030.pdf), which is HFC-134a.
Using freeze 12 is 3/4 of the way to a R134a system so you might as well go through and replace everything, the expansion valve and receiver/drier (accumulator) particularly if you're replacing the compressor too.

 

I used Duracool on my previous car. The benefit to Duracool is that it is compatible with either oil from R12 or R134 (which do not mix). The idea is that you do not need to flush your system to use Duracool. They also claim that the molecules are larger than R134 so it is less likely to leak. Maybe so, but I fixed the leak before I added the Duracool and it worked great for me.

 

I used the cheapo conversion kit from Wally World and it works a treat - even in the Arizona heat and no rear on the 4Runner it still blasts super cool air. I have a leak somewhere and have to top it up about once every couple of months, but no biggie for a trail and occasional use rig.

 

AFAIK duracool and other R12a conversions are mostly propane!!! Not something that I'd like to have in my engine bay and cabin.

R134a conversions aren't too hard or expensive, why not do it properly? If you're lazy or cheap, just vacuum the system for 30mins (instead of 15) and then charge it up.