The Proper Way to Charge an AC Unit with Refrigerant

Routine Maintenance

The first step in charging your unit is to replace the air filter, clean the evaporator and condenser coils. Adding refrigerant when these items are damaged or malfunctioning will further damage the AC unit.


Check the unit for obstructions that can be found in the blower and condenser fans. These parts of the AC unit keep hot air moving from inside the unit to the outside atmosphere. Any obstructions will impede the release of hot air which can cause the unit to overheat.


Complete an inspection of other components of the unit. Check for leaking ducts, loose electrical connections, and missing insulation. The overall efficiency of your unit will increase when these items are in top working condition.

Type of Refrigerant

The unit’s equipment operating guide supplied by the manufacturer will tell you the type of refrigerant to use. Systems may also have this information in the electrical control box or it may be found on the unit’s cabinet. R-22 and R410A are usually used.

Charging Connections

For adequate safety and for an efficient charge normal inverted flare valve connections may be used. These will often be provided with quick connect adaptors to decrease the loss of refrigerant during the charging process and the chance of injury.

Turn the Unit Off

The unit must be turned off at the thermostat.

Power Down

The unit will have a fused disconnect or circuit breaker assigned to it. Remove the fuses and/or turn the breaker off

Hook Up the Gauges

Attach the gauges to the valve connections. The blue hose will typically be attached to the low pressure side and the red hose is attached to the high pressure side. After the gauges are hooked up, turn on the A/C unit and wait a few minutes for the system to stabilize itself.

Read Your Gauges and Allow the System to Charge

charge an AC unit 2As the system is stabilizing with the gauges connected and if the system is low, then the reading on the blue (low pressure) hose should have dropped. You must verify that the unit requires charging by using the temperature gauge attached to the low pressure side. Recharge the unit if the temperature on the blue (low pressure) side do not match the manufacturer’s recommended specifications.

 Complete a Cooling Cycle

Turn the unit on and observe a complete cooling cycle. If temperatures return to normal, turn off power to the unit, and remove the gauges.