I have a Goodman 3.5 ton heat pump model A42-00 about 10 years old which had stopped blowing heat. The tech said the unit was "bone dry" and said he added 12 pounds of freon. Unit is working now but I am doubtful that he added that much freon. How could I have verified this? Should he have documented this? I have no invoice and paid cash. Should he have showed me the gauges? What is the procedure (if any) for documenting how much freon is required and then added?