I said R-12, I meant R-22 (I was half asleep). It would almost be cheaper (and a hell of a lot easier) to change out the current condensing unit. They usually are precharged with 25 feet worth of freon. Most installations have 50 feet or more so you would need to top it off with freon. I am going to tell my secret when it comes to purchasing condensing units at a great price.
Chad Supply - They have an 800# but I don't know it. I do have the local number here in Jax, FL. Its (904) 739-3633. They are a nationwide company so odds are they are in your area. Just call and order you a catalog.
Starting price for a 1 1/2 ton Maratherm Condensing unit is $320.00 (that's precharged with R-22). It goes up about $50 per additional ton. This includes delivery to your site. Not bad, huh?
Well I don't frequently visit these old posts so sorry if I didn't catch you in time. If you have any other questions post them at the top of the board. Good Luck!