hi, i am a student of lincoln tech. i was told by one of my instrutor that undercharge and overcharge. we don't need to use superheat or subcooling. just use temp difference between return air and supply air like for a/c would be 20F difference. is it ture? does this apply to refrigeration system. how? anyone show me example for detail please? like use R-134a for medium-temp refrigerator. if outside temp is 95F. what's the low-side gauge reading would be? what's the high side? is it low-side pressure related to ambient temp?