Camshaft

My 92 AC is not blowing as cold as fast in my car. It gets pretty cool, but not cold. I have the testing stuff for a R-134a setup, and a few cans of R-12. Will the testing stuff work on an R-12 setup without damaging anything? I have heard of a guy switching to 134a and then putting in a special type coolant that makes it really cold, just as cold as before. Ideas?