It is my understanding that the correct way to charge an R22 system without a TXV is by getting the actual superheat to match the target superheat. It is also my understanding that the target superheat in Fahrenheit is determined by the equation:
Target superheat = (3 x Indoor Wet bulb temperature 80 Outdoor ambient temperature)/2
And the actually superheat:
Actually superheat = Suction line temperature the refrigerant boiling point for the measured suction line pressure.
Ive found different sources that claim this is the correct method including the manual for my condensing unit. Nonetheless I have yet to meet an HVAC technician who agrees with this or for that matter even had a web bulb thermometer or digital psychrometer in their possession. The last technician said it was good enough to get around ten degrees of actual superheat no matter what.
What is the truth?