Before trying Red-Tex find and study the info on it. It's primarily propane, does indeed work well as a car refrigerant, but has the disadvantage that it's a gas at normal pressures/temperatures and highly explosive when mixed with air. So in using it in an automotive refrigeration system you're piping an explosive gas into a metal/glass box in which you'll be sitting. Any leak, say in a minor crash ...
The following link has a pretty good discussion and there's a YouTube video a few posts down with a demo of propane in a car:
My '11 Acadia has a decent a/c temp, but I'd like to try and get it a bit colder. I know I should just check and top off what's needed, but I have been reading on Red Tek's site saying that their refrigerant operates at a lower head pressure, improved cooling properties and requires much less...
gmtnation.com
There's a reason it's not used commercially for car A/C.