[Richard]

Hang on chaps. Amperage and gauge pressures are good ways to coarsely adjust the refrigerant level.

I am not trying to be all AC know it all on you. I am trying to make sure that you stay as a cool as a possible in the the coach. Or better yet, that your better half stays cool. My bride doesn't do heat. Happy wife, happy life. That is the absolute driver of everything I know about AC systems.

Do some research on capillary systems, as opposed to expansion valve systems (TXV), and use the superheat method to determine how much refrigerant to add. It's not hard and it is the most accurate way to charge a system.