Check the unit’s nameplate for the correct refrigerant type
Confirm the system is actually low on refrigerant
Turn off power to the AC unit
Wear safety glasses and gloves
Connect manifold gauges to the service ports
Attach the refrigerant cylinder to the charging hose
Purge air from the hose
Start the AC and let it run
Open the low-side valve slowly
Add refrigerant in small amounts
Monitor pressure and temperature while charging
Stop when the system reaches the specified charge
Close the valves and disconnect the gauges
Replace service port caps
Restore power and test operation
Use a licensed HVAC technician if required by law