I am sure the system had R-12 at some time, but the system was empty when I got the car.

Since then I replaced the compressor and the drier, and converted to R134.

There is a pressure switch on the drier, but from my reading I have found that it just prevents the compressor from coming on if there is no freon.

But also from my reading I found that the climate control system does monitor the temperature of the evaporator, so the controller could cycle the compressor to control the temperature of the evaporator.

In any case mine does not appear to cycle and I an trying to determine if that is normal.