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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 Heating, Ventilation and Air Conditioning (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.

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 can take 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: The A/C Cooldown test which can be initiated on the MTC or ATC system is not a valid test to determine A/C performance. It is intended to be only used at the assembly plant and should not be used at a dealer or repair facility. Use only the following procedure to check A/C performance.

1. Make sure the following conditions are met in the area where this test is to be performed:
- Maximum ambient temperature: 43.3°C (110°F)
- Minimum ambient temperature: 15.5°C (60°F)
- Maximum relative humidity: 90%
- Minimum relative humidity: 20%

2. Using a scan tool, check for Diagnostic Trouble Codes (DTCs) related to the Controller Area Network (CAN) data bus, Telematics Gateway (TGW), A/C heater module, Body Control Module (BCM) and Powertrain Control Module (PCM). If no DTCs are found, go to Step 3. If any DTCs are found, repair as required, then proceed to Step 3.
3. Operate the heating and A/C system under the following conditions.
- Engine at normal operating temperature
- Engine at normal idle speed
- No sun-load in the cabin of the vehicle
- Vehicle doors and windows closed
- Transmission in Park or Neutral with the park brake On.
- A/C heater controls set to Recirculation mode, 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
- All panel outlet vanes open and positioned straight rearward

NOTE: If the following step is not performed, the results of this test will not be accurate.

4. Using a scan tool, operate the engine cooling fans at high speed.
5. Insert a thermometer in the driver side center panel air outlet and operate the A/C system until the thermometer temperature stabilizes or a minimum of five minutes.

NOTE: This procedure requires you to know what the temperature and relative humidity is in your location at the time of the test. This information can be obtained from multiple sources, such as the internet or local news media.

6. With the A/C clutch engaged, compare the observed panel outlet air temperature along with the ambient temperature of the work area and the relative humidity to the Maximum Panel Outlet Temperature chart.
7. If the air outlet temperature fails to meet the specifications shown in the Maximum Panel Outlet Temperature chart, see the A/C System Diagnosis table.



Figure 1 - Maximum Panel Outlet Temperature
A/C SYSTEM DIAGNOSIS










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