question regarding r12
 

Well, the question I have isn't really specific to this Gen. or Blazer or even vehicle in general. What I have is a sneaking suspescion(sp) that when I loaned out my new #30 can of R12 that the guy that actually had use of it may have taken all of the r12 out in a recovery unit and replaced it with friggen water for all I know. I found out later that it was not this friend of mine who actually had use of the freon but this other loser.
At any rate, I just got that feeling that "something" was done with it. It was full 30 lbs and expected to have 4 or 5 lbs to have been used when I got it back and have it weigh under 30 obs. It still weighs 30 lbs. and actually a couple pounds over. One of the reasons I fear the worst here. So what is the best way to check this? I am sure it will involve connecting gauges to the one low side gauge, open and see what it reads maybe, but how do I determine that it it true virgin r12? Is there anyway to tell the dif between the 12 and the 134? I want to sell the can but don't want to sell it until I know it is what it is suppose to be.
tia

If its not a recovery tank (with two valves) it will not receive a backflow and will be pure R12.
If it is a recovery tank, thats trouble. The only real way to tell if you have any 134a present is to have a special leak detector that only picks up HFC.