Lyle my honest opinion is that you have a
lot more reading to do before embarking on this and filling the system up. You can't just dump refrigerant in and hope it works. Here is a good place to start:
http://www.peachparts.com/shopforum/showthread.php?t=297462
Huge list of very informative A/C DIY threads:
http://www.peachparts.com/shopforum/showthread.php?t=142408
First off, a vacuum test is not a very efficient way to test the integrity of an A/C system (certainly not a little handheld mityvac). The seals will not behave the same way under vacuum as they do under high pressure. It is a good way to initially boil off any moisture (and no way will you get that much pressure with a mityvac), but then you need to flush the entire system with dry air. You can pressurize the system with dry air (dry nitrogen, CO2 or R22) and see if it holds and THAT will be a decent test before dumping R12 into the system. Second, you will need to replace at least the receiver dryer after pulling a vacuum and flushing if its been sitting for that long. Third, you are required to have an EPA license (easy to get) to purchase R12 in the United States. Freeze 12 does not require a license because it is not R12. The reason R12 was banned/replaced is because it is very harmful to the atmosphere, and that is why they take this stuff so seriously.
You can't just wing it and vent the R12 into the atmosphere in a trial-and-error process. I'm sorry if I'm coming off as extremely critical, but between this thread and your other one it is clear you need to read up a lot more on the whole process. R12 is a potent chemical. There are some extremely knowledgeable members on this board (I would not consider myself one, at least not for A/C...I only have a basic understanding of the system) who I'm sure will be happy to help out.