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A/C Performance






A/C PERFORMANCE

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.

A/C PERFORMANCE TEST

WARNING: Refer to the applicable warnings and cautions for this system before performing the following operation Warning and Caution . Failure to follow these instructions may result in possible serious or fatal injury.

CAUTION: The use of an A/C recycling/charging station for purposes of determining the actual charge level of an A/C system is not recommend. Service recycling/charging stations do not reflect the correct amount of refrigerant charge in the A/C system after a single "reclaim" cycle. Tests have shown that it takes up to two or more "reclaim" cycles to remove all of the refrigerant charge, depending on the equipment being used. Use only the following procedure for determining the proper charge level.

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. Check for Diagnostic Trouble Codes (DTCs) using a scan tool. If no DTCs are found in the Powertrain Control Module (PCM) or Engine Control Module (ECM), depending on engine application, Cabin Compartment Node (CCN) or the Totally Integrated Power Module (TIPM), go to 2. If any DTCs are found, repair as required, then proceed to 2.
2. Connect a tachometer and a manifold gauge set or an A/C recycling/charging station.

NOTE: The ambient air temperature of the vehicle and the location where the vehicle will be tested must be a minimum of 21° C (70° F) before performing this test. Also the evaporator temperature sensor must be a minimum of 13° C (55° F) for this test as well. Place the vehicle in the testing area until the temperature within the vehicle reaches a minimum of 21° C (70° F) prior to conducting the A/C Performance Test.

3. Operate the heating-A/C system under the following conditions.
- Engine at idle and operating temperature
- Doors or windows open
- Transmission in Park or Neutral with parking brake set (depending on application)
- A/C-heater controls set to Recirculation mode (max-A/C), full cool, panel mode, high blower and with A/C compressor engaged. If the A/C compressor does not engage, see the A/C System Diagnosis table.

4. Insert a thermometer in the driver side center panel air outlet and operate the vehicle a minimum of ten minutes to allow the thermometer temperature to stabilize.

NOTE: This procedure requires the technician to know what the temperature and relative humidity is at the time of the test. The temperature must be combined with the relative humidity to calculate the apparent ambient air temperature, when temperatures are above 21° C (70° F). Use the current ambient temperature and the relative humidity in your location. This information can be obtained from multiple sources, such as the internet or local news media.

5. With the A/C clutch engaged, compare the air temperature at the center panel outlet and the A/C compressor discharge pressure (high side) to the A/C Performance Temperature and Pressure chart. The A/C clutch may cycle, depending upon the ambient temperature and humidity. If the A/C clutch cycles, use the readings obtained before the clutch disengaged.
A/C PERFORMANCE TEMPERATURE AND PRESSURE






6. If the air outlet temperature fails to meet the specifications in the A/C Performance Temperature and Pressure chart, or if the A/C compressor discharge pressure is high, see the A/C System Diagnosis table.
A/C SYSTEM DIAGNOSIS










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