There is a website that offers a very short course & test to get certified by the EPA as a motor vehicle air conditioning technician. EPATest.com

It costs all of $19.95 to take the test. The course material is free online or a few $ if you want a paper booklet mailed to you. You want the "section 609" stuff. Pass the test, get a cert number and you're legal to buy real Freon, aka R-12, aka CFC-12 in small cans. It's available on eBay & other places. You can top up your own car's system completely legally. If you work on another person's car "for compensation" you're supposed to use a freon recovery system. All of the legal stuff is explained in the course. It took me about 1 1/2 hours undisturbed to read through the ebooklet and pass the 25 question test: 100%. All multiple choice and maybe 18 of those were verbatim from the book. It's open book and you can have another browser window open and do a search to find the answers - legally.

No need to retrofit with R-134a or experiment with "Freeze 12" or other bogus stuff.

Cool,

__________________
Norm in NJ
Next oil change at 230,000miles