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.Refer to the applicable warnings and cautions for this system before performing the following operation (refer to 24 - HEATING & AIR CONDITIONING/PLUMBING - WARNING) and (refer to 24 - HEATING & AIR CONDITIONING/PLUMBING - CAUTION). Failure to follow the warnings and cautions could result in possible personal injury or death.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.The work area ambient temperature must be above 21° C (70° F) and the evaporator temperature must be above 13° C (55° F) prior to conducting the A/C Performance Test.Check for diagnostic trouble codes using a scan tool. If no DTCs are found in the powertrain control module (PCM) or engine control module (ECM) (depending on engine application) or the totally integrated power module (TIPM), go to STEP 2. If any DTCs are found, repair as required, then proceed to STEP 2.Connect a tachometer and a manifold gauge set or an A/C recycling/charging station.Operate the heating-A/C system under the following conditions.Engine at idle and operating temperatureDoors or windows openTransmission 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 chart.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.With the A/C compressor 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 compressor clutch may cycle, depending upon the ambient temperature and humidity. If the clutch cycles, use the readings obtained before the clutch disengaged.Ambient Temperature21° C (70° F)27° C (80° F)32° C (90° F)38° C (100° F)43° C (110° F)Air Temperature at Center Panel Outlet6 -15° C (42 - 59° F)7 -18° C (45 - 64° F)9 - 21° C (48 - 69° F)11 - 22° C (52 - 72° F)13 - 24° C (56 - 75° F)A/C High Side Pressure1034 - 1896 kPa (150 - 275 psi)1207 - 2068 kPa (175 - 300 psi)1379 - 2241 kPa (200 - 325 psi)1551 - 2413 kPa (225 - 350 psi)1724 - 2241 kPa (250 - 375 psi)A/C Low Side Pressure214 - 365 kPa (31 - 53 psi)248 - 407 kPa (36 - 59 psi)283 - 476 kPa (41 - 69 psi)317 - 483 kPa (46 - 70 psi)359 - 496 kPa (52 - 72 psi)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, refer to the A/C System Diagnosis chart.ConditionPossible CausesCorrectionRapid A/C compressor clutch cycling (ten or more cycles per minute).1. Low refrigerant system charge.1. See Refrigerant System Leaks in this group. Test the refrigerant system for leaks. Repair, evacuate and charge the refrigerant system as requiredEqual pressures, but the compressor clutch does not engage.1. No refrigerant in the refrigerant system.1. See Refrigerant System Leaks in this group. Test the refrigerant system for leaks. Repair, evacuate and charge the refrigerant system as required.2. Open fuse.2. Check the fuse in the junction block. Repair the shorted circuit or component and replace the fuse as required.3. Inoperative A/C compressor clutch field coil.3. See A/C Compressor Clutch Field Coil in this group. Test the compressor clutch field coil and replace as required.4. Improperly installed or inoperative A/C pressure transducer.4. See A/C Pressure Transducer in this group. Test the transducer and replace as required.5. Improperly installed or inoperative Evaporator Temperature Sensor.5. See Evaporator Temperature Sensor in this group. Correctly install or test and replace the sensor as required.6. Inoperative A/C-heater control, totally integrated power module (TIPM) or PCM/ECM.6. Refer to the appropriate Electrical Diagnostic Procedures for testing of the A/C-heater control, TIPM or PCM/ECM. Test the module and replace as required.Normal refrigerant pressures, but A/C Performance Test air temperatures at center panel outlet are too high.1. Excessive refrigerant oil in system.1. See Refrigerant Oil Level in this group. Recover the refrigerant from the refrigerant system and inspect the refrigerant oil content. Restore the refrigerant oil to the proper level as required.2. Temperature control cable improperly installed or inoperative.2. See Temperature Control Cable this group. Inspect the cable for proper operation. Replace the cable as required.3. Blend door inoperative or sealing improperly.3. See HVAC Housing in this group. Inspect the blend door for proper operation and sealing. Repair as required.4. Blend door not in full cold position.4. See Temperature Control Cable this group. Inspect the cable for proper operation. Replace the cable as required.The low side pressure is normal or slightly low, and the high side pressure is too low.1. Low refrigerant system charge.1. See Refrigerant System Leaks in this group. Test the refrigerant system for leaks. Repair, evacuate and charge the refrigerant system as required.2. Refrigerant flow through the A/C evaporator is restricted.2. See A/C Evaporator in this group. Replace the restricted A/C evaporator as required.3. Inoperative A/C compressor.3. See A/C Compressor in this group. Replace the compressor as required.The low side pressure is normal or slightly high, and the high side pressure is too high.1. A/C condenser air flow restricted.1. Check the A/C condenser for damaged fins, foreign objects obstructing air flow through the condenser fins, and missing or improperly installed air seals. Clean, repair, or replace components as required.2. Refrigerant flow through the receiver/drier is restricted.2. See Receiver/drier in this group. Replace the restricted receiver/drier as required.3. Inoperative radiator cooling fan.3. Test the radiator cooling fan and replace as required. Refer to Group 7.4. Refrigerant system overcharged.4. See Refrigerant System Charge in this group. Recover the refrigerant from the refrigerant system. Charge the refrigerant system to the proper level as required.5. Air in the refrigerant system.5. See Refrigerant System Leaks in this group. Test the refrigerant system for leaks. Repair, evacuate and charge the refrigerant system as required.6. Engine overheating.6. Test the engine cooling system and repair as required. Refer to Group 7.The low side pressure is too high, and the high side pressure is too low.1. Accessory drive belt slipping.1. Inspect the accessory drive belt condition and tension. Replace the accessory drive belt or tensioner as required. Refer to Group 7.2. Inoperative A/C expansion valve.2. See A/C Expansion Valve in this group. Replace the valve as required.3. Inoperative A/C compressor.3. See A/C Compressor in this group. Replace the compressor as required.The low side pressure is too low, and the high side pressure is too high.1. Restricted refrigerant flow through the refrigerant lines.1. See Liquid Line, Suction Line and Discharge Line in this group. Inspect the refrigerant lines for kinks, tight bends or improper routing. Correct the routing or replace the refrigerant line as required.2. Restricted refrigerant flow through the A/C expansion valve.2. See A/C Expansion Valve in this group. Replace the valve as required.3. Restricted refrigerant flow through the A/C condenser.3. See A/C Condenser in this group. Replace the restricted condenser as required.