Thank you so much for all the time you guys have put into this discussion. I think you've convinced me that converting to R-134a certainly isn't a DIY job without gauges and experience, and that R-134a doesn't cool as much as R-12. So, my question is this: assuming that I don't have any leaks in my system (which I'm not sure of), how long will a R-12 charge last me? The car is a 1983 with 120,000 miles on it and I really don't know how much longer I will own this car. I definitely am willing to pay the extra to have the refrigerant that this car was meant to have and to have cooler air, but I don't want to have to recharge this system too often. I don't know when the last time the A/C was serviced because it was my dad's car and he doesn't know either.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside