I have a couple of old cars that have leaks in the AC at the compressor shaft. As you might guess, I have no money. The cost of repair is more than the value of the car, so I'm just adding a little R-134a a couple of times during the summer. I've got a digital thermometer that I stick in the air vent and add refrigerant until the temperature drops from 80 degrees to 52 degrees. At that point, I notice that adding more refrigerant doesn'nt do much for lowering the vent temperature. Eventually, I see that the condensation on the lines coming out of the evaporator begins to frost over so I stop and disconnect at that point.
This has worked well for me but I thought I would ask if you might know a better way. Like measuring the temperature of the compressor low pressure line about 4 inches from where it enters the compressor.
PJ