Connect the high-pressure gauge to the high-side service valve. Open the valve. Disconnect the condenser fan or block the airflow, or if it is a water-cooled system, shut off the flow of water. As the temperature rises, so does the head pressure. If the gauge goes over 10% above the correct head pressure and the control fails to shut off the compressor, disconnect the power and adjust the high-pressure control to a correct setting or replace the control if necessary.
CAUTION: Perform this check for a brief time only to prevent damage to the unit.