I have been following with interest the discussions on charging a unit using super heat and sub cool. Today while wiring up a Goodman 3 1/5 ton heat pump I read under the cover their recommendations on charging in the cool mode and the heat mode.
In the heat mode they said to use the hot gas method. Take the line temp between the compressor and the reversing valve. They said it should be 126 or 127 degrees ( can't remember which) degrees hotter than the ambient temperature outside. Too hot add gas and too cool remove some of the charge. Sounds like an easy way to do it and I am asking is this just something to get you in the ball park or is it a reliable way to check the charge. This unit uses R-22.
Another question is could you use this with a unit that uses say 134A with a different temperature adder.