A/C Performance Test

The air conditioning system is designed to provide the passenger compartment with low temperature and low specific humidity air. The evaporator, located in the heater 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 their 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.

WARNING: REFER TO THE APPLICABLE WARNINGS AND CAUTIONS FOR THIS SYSTEM BEFORE PERFORMING THE FOLLOWING OPERATION.

NOTE: Very specific instructions and conditions pertain to this procedure which are significantly different than procedures used in other vehicle applications. Follow each step in the order they are presented. Do not skip steps or change conditions from those stated or results will be adversely affected and invalid.

The compressor clutch is de-energized under any of the following conditions:
- Blocked compressor (thermal fuse in the pulley)
- Low pressure in the system
- Low evaporator temperature
- Hard acceleration (WOT)
- High coolant temperatures

1. Place the vehicle in the shade with all widows open.
2. Turn the temperature control to cold.
3. Select Fresh Air, not Recirculate and open all air conditioning duct louvers.
4. Start the vehicle and allow it to idle.
5. Turn the blower switch to the maximum blower speed setting and allow to operate for a short period of time before proceeding.
6. Perform an outlet temperature test as follows:
a. Turn the blower switch to the lowest blower speed setting.
b. Insert a thermometer into a center duct for at least five minutes.
c. With the engine running, duct temperature should not be less than 2° C (35° F) or than 12° C (54° F).

7. If the compressor has not cycled off and the duct temperature is less than 2° C (35° F) , check the evaporator temperature sensor and circuit by performing the ATC Function Test.
8. If duct output temperature is not within specifications, check the refrigerant system for leaks and proper refrigerant charge.