I'm in the exact same situation with my wifes car. The exception is that I know the leak is very minor , takes about 5 month's to leak down and I have the EPA 609 certification to handle R-12 freon. What I opted to do is buy some R-12 off of eBay, I got 7 14oz cans for ~$100., add about 1 lb and buy myself some time. In the mean time I'll buy a electronic A/C leak checker (eBay) ~$50., I bought some MAC guages and hoses $33.50 (eBay), and I'll buy a A/C vacuum pump ~$75.-$125. you guessed it eBay! and I will repair the A/C myself. As a former service rep for a new car dealership I can tell you this: good/honest A/C mechanics are hard to find, and there is alot of room for errors read: mis-diagnosis, return trips and more cost to the customer. "Hey, it's not my fault the A/C on your car keeps springing leaks" To make matters worse, A/C work is very expensive, the conversion van you spoke of most likely has rear air and possibly a rear evaporator core, it will probably hold 5 lbs of freon. Good luck with whatever you decide to do, if I were you I would get some recommendations from friends and family for a good repair shop. Also, The R134a does not cool as good as R12, worse at low engine/compressor speeds (hot, huumid, stop and go traffic) it works at a higher pressure and thus the chances leaks increase. The conversion, on late model cars and trucks is simply a couple of fittings that go on the high and low pressure schrader valves that prevent the accidental servicing of R12 after the conversion. Parts cost about $25. labor is about 15 minutes + flushing the R12 out (R12 and R134a DONOT mix).