A/C Performance Test

The air conditioning system is designed to provide the passenger compartment with low temperature and low humidity air. The evaporator, located in the HVAC housing on the dash panel below the instrument panel, is cooled to temperatures near the freezing point. As warm damp air passes through the cooled evaporator, the air transfers its heat to the refrigerant in the evaporator and the moisture in the air condenses on the evaporator fins. During periods of high heat and humidity, an air conditioning system will be more effective in the Recirculation Mode. With the system in the Recirculation Mode, only air from the passenger compartment passes through the evaporator. As the passenger compartment air dehumidifies, the air conditioning system performance levels improve.

Humidity has an important bearing on the temperature of the air delivered to the interior of the vehicle. It is important to understand the effect that humidity has on the performance of the air conditioning system. When humidity is high, the evaporator has to perform a double duty. It must lower the air temperature, and it must lower the temperature of the moisture in the air that condenses on the evaporator fins. Condensing the moisture in the air transfers heat energy into the evaporator fins and tubing. This reduces the amount of heat the evaporator can absorb from the air. High humidity greatly reduces the ability of the evaporator to lower the temperature of the air.

However, evaporator capacity used to reduce the amount of moisture in the air is not wasted. Removing some of the moisture out of the air entering the vehicle adds to the comfort of the passengers. Although, an owner may expect too much from the air conditioning system on humid days. A 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.

PERFORMANCE TEST PROCEDURE
Review Safety Warnings and Cautions before performing this procedure. Air temperature in the test room and in the vehicle must be 21° C (70° F) minimum for this test.

1. Connect a tachometer, a manifold gauge set or A/C recycling/charging station.
3. Set the mode control to the Recirculation Mode position, the temperature control to the full cool position, and the blower motor to the highest speed position.
3. Start the engine and hold the idle at 1,000 rpm with the A/C compressor clutch engaged.
4. The engine should be warmed up to operating temperature with the doors closed and windows open.
5. Insert a thermometer in the driver's side center panel A/C-heater outlet and operate the engine for five minutes.

A/C Low Pressure Switch - Typical:

6. The compressor clutch may cycle, depending upon the ambient temperature and humidity. If the clutch cycles, unplug the A/C low pressure switch wire harness connector from the switch located on the accumulator. Place a jumper wire across the terminals of the A/C low pressure switch wire harness connector.

Performance Temperature And Pressure:

7. With the compressor clutch engaged, compare the discharge air temperature and the compressor discharge pressure.
8. If the discharge air temperature fails to meet the specifications in the A/C Performance Temperature and Pressure chart, refer to the Pressure Diagnosis chart.

Pressure Diagnosis Part 1:

Pressure Diagnosis Part 2:

9. Compare the compressor discharge pressure to the Performance Temperature and Pressure chart. If the compressor discharge pressure is high, see the Pressure Diagnosis chart.