A/C Performance Test

An air conditioning performance test is the best way to determine whether the system is performing up to standard. This test also provides valuable clues as to the possible cause of trouble with the air conditioning system. The ambient air temperature in the location where the vehicle will be tested must be a minimum of 21 °C (70 °F) for this test.

NOTE: When connecting the service equipment coupling to the line fitting, verify that the valve of the coupling is fully closed. This will reduce the amount of effort required to make the connection.

1. Connect a tachometer to monitor the engine speed.
2. Remove the caps from the refrigerant system service ports and attach a manifold gauge set to monitor the refrigerant system pressures.
3. Set the heater-air conditioner controls so that the compressor is engaged, the air within the vehicle is being recirculated, the output air is directed through the panel outlets, the temperature control is in the full cool position, and the blower motor is operating at its highest speed.
4. Start the engine and allow the engine to operate for about five minutes or until it reaches normal operating temperature. Then hold the engine speed at 1000 rpm with the compressor clutch engaged. If the compressor clutch does not engage, proceed with diagnosis of the compressor clutch coil.
5. Close all the vehicle windows and doors.
6. Insert a thermometer in the left center panel outlet and operate the engine for five minutes.
7. With the compressor clutch engaged, record the left center panel outlet discharge air temperature, the discharge pressure (high side service port), and the suction pressure (low side service port). The compressor clutch may cycle, depending upon the ambient temperature and humidity If the clutch cycles, use the readings obtained before the clutch disengaged.

Performance Temperature And Pressure:

8. Compare the discharge air temperature reading to the Performance Temperature and Pressure chart. If the temperature reading is high, check the refrigerant system for leaks and proper refrigerant charge level.