A/C Performance Test

The A/C system is designed to provide the passenger compartment with low temperature and low humidity air. The A/C evaporator, located in the HVAC housing is cooled to temperatures near the freezing point. As warm damp air passes over the fins of the A/C evaporator, the air transfers its heat to the refrigerant in the evaporator coils and the moisture in the air condenses on the evaporator fins. During periods of high heat and humidity, an A/C system will be more effective in the Recirculation mode (max-A/C). With the system in the Recirculation mode, only air from the passenger compartment passes through the A/C evaporator. As the passenger compartment air dehumidifies, the A/C system performance levels rise.

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 A/C system. When humidity is high, the A/C 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 coils. This reduces the amount of heat the A/C evaporator can absorb from the air. High humidity greatly reduces the ability of the A/C evaporator to lower the temperature of the air.

However, evaporator capacity used to reduce the amount of moisture in the air is not wasted. Wringing 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 A/C system on humid days. A performance test is the best way to determine whether the system is performing up to design standards. This test also provides valuable clues as to the possible cause of trouble with the A/C 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.

WARNING: REFER TO THE APPLICABLE WARNINGS AND CAUTIONS FOR THIS SYSTEM BEFORE PERFORMING THE FOLLOWING OPERATION. FAILURE TO FOLLOW THE WARNINGS AND CAUTIONS COULD RESULT IN POSSIBLE PERSONAL INJURY OR DEATH.

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.
- 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. Check for diagnostic trouble codes using a DRBIII(R) scan tool. If no DTCs are found in the engine control module (ECM), go to Step 2. If any DTCs are found, repair as required, then proceed to Step 2.
2. Place the vehicle in the shade and operate the heating-A/C system under the following conditions.
- Engine at idle at operating temperature
- All doors or windows open
- Transaxle in Neutral
- All A/C duct louvers open
- A/C-heater controls set to fresh air (NOT Recirculate), full cool, panel mode, high blower and with A/C compressor engaged.

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

3. Insert a thermometer in the driver side center panel air outlet and operate the A/C system until the thermometer temperature stabilizes.
4. With the A/C compressor clutch engaged, duct temperature should not be less than 2° C (35° F) or more than 12° C (54° F). The compressor clutch may cycle, depending upon the ambient temperature and humidity. If the clutch cycles, use the readings obtained before the clutch disengaged.
5. If the A/C compressor clutch 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.

A/C System Diagnosis Part 1:

A/C System Diagnosis Part 2:

A/C System Diagnosis Part 3:

6. If the air outlet temperature fails to meet the specifications, refer to the A/C System Diagnosis chart.