A correctly functioning R-12 system will out perform a R-134a conversion, Make sure your system is free of leaks and correctly charged, If you have an auxillary fan make sure it operates when a/c is switched on, condenser relatively free of debris, a/c controls and vents in good working order. You can still get R-12 in the states but it will be more costly than in Mexico. If your a/c system is in descent shape, you would not have to go to Mexico very often.