I did some research and was advised to convert my 94 Toyota with a non functioning R12 system to 134A. I took the opportunity to learn about auto AC and went about it myself. It took a long time and I spent much time on the internet with some real knowledgeable AC people.
The one big thing I learned is when someone says AC just needs a charge it is BROKEN unbroken systems to not leak! If it is broken it will likely be expensive to redo.
2nd big thing I learned is I should not have converted to 134a !!!! Against all conventional wisdom.
At one time R12 was rare and expensive!! This is no longer the case, most of the cars on the road today came with 134a and many people horded R12 and now have no market for it, so the price is dropping and dropping. Currently $25/30 a can. Contrary to popular belief R12 is still being manufactured. Yes I know in the US they stopped manufacturing it, well the US is not the whole world and some of it finds it's way here.
I also know someone that says just put new fittings on and dump some gas in there and your good to go. Get the stuff from Wal Mart, snake oil in a can with leak killer. In the 4 years I have known him he has replaced 2 AC compressors in his big rig, but he never mentions that!