Turn off power to the AC unit at the thermostat and breaker
Confirm the system uses the correct refrigerant type listed on the unit nameplate
Check for leaks and repair them before adding refrigerant
Connect a manifold gauge set to the service ports
Attach the refrigerant cylinder to the center hose of the gauge set
Purge air from the hoses
Start the AC system and let it run
Read the pressure and temperature values
Add refrigerant slowly through the low-side port only
Monitor system pressures and superheat or subcooling as required
Stop adding refrigerant when the system reaches the correct charge
Close the manifold valves and disconnect the hoses
Replace service port caps tightly
Restore power and verify normal operation
Use a licensed HVAC technician if you are not trained or if the system is sealed or under warranty