Wal-Mart sells a pressure gauge for not much money, that will show the changes in pressure as the system cycles on and off. The gauge is numbered, and color coded. It's helped me a lot.

I used a similar product, I think it was Interdynamics, but was only 134A and oil. I had to add two cans, but the system works great now. It cycles on and off at about 40-42 F.

95 Contour Zetec, ATX (wrecked, sitting in the barn) 95 Mystique Zetec, MTX 2000 Taurus SEL 3.0L Duratec 1994 Crown Victoria LX 4.6 V8 1993 Chevy Silverado 4.3 V6