Don't forget to mention that they are also illegal for use in mobile AC equipment. Also don't forget to change the service fitting on your AC system so that in the future a tech does not recover your propane into his 50 lb cylinder of pure R12 and lose $500 dollars worth of refrigerant. Of course thats the "best case" scenario - he could also not discover that his R12 supply had been contaminated and proceed to dispense a contaminated and illegal mix of hydrocaron based refrigerants in his customers cars.

Pulling a deep vacuum is a trivial task if you have a vacuum pump and a A/C system that is not leaking - pumps are available for about $200 new and they can be rented at many rental shops for $10-15.

Bulk R12 is now under $10 a pound on e-bay and 12 oz cans sell for $15-30 dollars per can. You can recharge your system for a total of $30-$60 - is it really worth it to mess around with HC based refrigerants? It's amazing to me that somebody can take the time to do the research on this topic and come away with the conclusion to introduce anything but the correct R12 into their system.

I'd also like to disagree with Dave regarding adding oil to a system that has a small leak - my service literature does not recommened this procedure and I've never added ANY oil when topping off A/C systems in cars. My A/C recovery equipment has an oil seperator with a sight glass bowl that shows how much oil has been removed during a recovery operation - the amount of oil removed in a total evacuation, as best I can tell, is about 1/50th of an ounce. The oil does not mix with the gas and for the most part it tends to stay in the system unless you have a massive leak.

Good luck - Tim