George,
If he just checked the Freon pressures, he is a hack! No wonder he is
so fast, it is easy to do a half assed job quickly. Every manufacturer
of AC equipment that I am familiar with uses suction superheat charts
to charge systems with piston metering devices and liquid subcooling
charts to charge systems with expansion valve metering devices.
If he checked the pressures, and added Freon, he did it wrong! He
should have checked the indoor wet bulb temperature, the outdoor dry
bulb temperature, the suction line or liquid line temperature
(depending on metering device) and the pressures. Then he can
determine if the charge is correct.

Stretch