PLEASE DO NOT TOP OFF AN R12 SYSTEM WITH FREEZE12!!!!!!!!
There is a very valid reason for this. What happens is someone comes along and recovers the refrigerant from that system resulting in the contamination of whatever R12 is in their container.
The ONLY R12 we have left is what is on the shelves and what we can recover and recycle.
PLEASE DON'T CONTRIBUTE TO THE CONTAMINATION OF OUR REMAINING R12 SUPPLY!!!!!!!!!!!!!!!
A great way that shops look for leaks and is approved by the EPA is 2 oz. of R22 and then pressurize to a few hundred pounds with nitrogen. This is a great way because you have high pressure to find leaks, even on the low side with a sniffer.
Another approach would be a little R12 and UV dye with a UV light.
Please don't use Freeze 12, or even get it near an R12 system.
Have a great day,