If you are going to refill it and your in texas I HIGHLY RECCOMEND, not converting to 134a, that is, unless you like being warmer than you could be, blowing up your AC system, replacing the pump, and still effectively having less effeciency and cooling power than R12
TRUST ME, the R12 is worth the money, It is also a more reliable refrigerant, and runs at lower pressures and creates less wear on the system, if its already converted to 134a and working then just stay with that, but if its not converted, DONT convert it.
And R12 is not bad for YOU just the O-zone layer. But Mr. Ozone layer, does not have to ride around in a hot ass datsauna.