I'll answer the second question first. Most auto AC shops can get (or have)
R12. But it is expensive. Anyone who gets the proper licence can get it, but
it is no longer available in 1lb cans.
To convert to R134, first make sure that all the components are in good shape.
R134 runs at slightly higher pressures than R12. Replace any components that
are iffy.Depending on the age of the car and the make of the compressor, the
compressor may have to be replaced, but usually not. Flush the system,
because not all R134 oils are compatible with R12. Evacuate the system (use a
vacuum pump), and make sure it hold a vacuum for 30 minutes. If it doesn't,
find and repair the leak. Once it will hold the vacuum, you can install the
R134. Start with about 10% less than called for with R12. For some cars, you
may want to replace the expansion valve. It is cheap, and one that is
calibrated for R134 will result in better cooling.
R134 also gives off more heat, so make sure that the radiator is good.
Maynard
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