DIAGNOSIS AND TESTING
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 (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.
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 using a scan tool. If no DTCs are found in the powertrain control module (PCM) or engine control module (ECM), depending on engine application, go to STEP 2. If any DTCs are found, repair as required, then proceed to STEP 2.
2. Connect a tachometer and a manifold gauge set or an A/C recycling/charging station.
3. Operate the heating-A/C system under the following conditions.
- Engine at 1,000 rpm at operating temperature
- Door 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 chart.
4. Insert a thermometer in the driver side center panel air outlet and operate the A/C system until the thermometer temperature stabilizes.
5. 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 Air Temperature | 21° C (70° F) | 27° C (80° F) | 32° C (90° F) | 38° C (100° F) | 43° C (110° F) |
| Air Temperature at Center Panel Outlet | 7° C (45° F) | 7° C (45° F) | 13° C (55° F) | 13° C (55° F) | 18° C (64° F) |
| Compressor Inlet Pressure at Service Port (Low Side) | 138 to 207 kPa (20 to 30 psi) | 172 to 241 kPa (25 to 35 psi) | 207 to 276 kPa (30 to 40 psi) | 241 to 310 kPa (35 to 45 psi) | 276 to 345 kPa (40 to 50 psi) |
| Condensor Outlet Pressure at Service Port (High Side) | 1034 to 1724 kPa (150 to 250 psi) | 1379 to 2068 kPa (200 to 300 psi) | 1724 to 2413 kPa (250 to 350 psi) | 1999 to 2689 kPa (290 to 390 psi) | 2413 to 2965 kPa (350 to 430 psi) |
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, refer to the A/C System Diagnosis chart.
| Condition | Possible Causes | Correction |
| Rapid A/C 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, if required. |
| Equal pressures, but the A/C 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, if required. |
2. Open fuse. | 2. Check the fuses in the power distribution center and the junction block. Repair the shorted circuit or component and replace the fuses, if required. Refer to Group 8. | |
3. Inoperative A/C clutch field coil. | 3. See A/C Compressor Clutch in this group. Test the A/C clutch field coil and replace, if required. | |
4. Inoperative A/C clutch relay. | 4. See A/C Clutch Relay in this group. Test the A/C clutch relay and relay circuits. Repair the circuits or replace the relay, if required. | |
5. Improperly installed or inoperativey A/C low pressure switch. | 5. See A/C Low Pressure Switch in this group. Test the A/C low pressure switch and tighten or replace, if required. | |
6. Inoperative A/C high pressure switch (diesel engine application). | 6. See A/C High Pressure Switch in this group. Test the A/C high pressure switch and replace, if required. | |
7. Inoperative A/C pressure transducer (gasoline engine application). | 7. See A/C Pressure Transducer in this group. Test the A/C pressure transducer and replace, if required. | |
8. Inoperative powertrain control module (PCM) or engine control module (ECM), depending on engine application. | 8. Refer to the proper Diagnostic Procedures manual for testing of the PCM or ECM. Test the PCM or ECM and replace, if required. | |
| Normal 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, if required. |
2. Blend door actuator improperly installed or inoperative. | 2. See Blend Door Actuator in this group. Inspect the actuator for proper operation and replace, if required. | |
3. Blend-air door inoperative or sealing improperly. | 3. See HVAC Housing in this group. Inspect the blend-air door for proper operation and sealing and correct, if 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, if required. |
2. Refrigerant flow through the A/C accumulator is restricted. | 2. See A/C Accumulator in this group. Replace the restricted accumulator, if required. | |
3. Refrigerant flow through the A/C evaporator is restricted. | 3. See A/C Evaporator in this group. Replace the restricted A/C evaporator, if required. | |
4. Inoperative A/C compressor. | 4. See A/C Compressor in this group. Replace the A/C compressor, if 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. Inoperative radiator cooling fan. | 2. Test the radiator cooling fan and replace, if required. Refer to Group 7. | |
3. Refrigerant system overcharged. | 3. See Refrigerant System Charge Level in this group. Recover the refrigerant from the refrigerant system. Charge the refrigerant system to the proper level, if required. | |
4. Air in the refrigerant system. | 4. See Refrigerant System Leaks in this group. Test the refrigerant system for leaks. Repair, evacuate and charge the refrigerant system, if required. | |
5. Engine overheating. | 5. Test the engine cooling system and repair, if 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. Tighten or replace the accessory drive belt, if required. Refer to Group 7. |
2. Inoperative A/C orifice tube. | 2. See A/C Orifice Tube in this group. Replace the liquid line, if required. | |
3. Inoperative A/C compressor. | 3. See A/C Compressor in this group. Replace the A/C compressor, if 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 A/C Discharge Line in this group. Inspect the refrigerant lines for kinks, tight bends or improper routing. Correct the routing or replace the refrigerant line, if required. |
2. Restricted refrigerant flow through the A/C orifice tube. | 2. See A/C Orifice Tube in this group. Replace the liquid line, if required. | |
3. Restricted refrigerant flow through the A/C condenser. | 3. See A/C Condenser in this group. Replace the restricted condenser, if required. |
HEATER PERFORMANCE
Before performing the following tests, refer to Group 7 - Cooling for the procedures to check the engine coolant level and flow, engine coolant reserve/recovery system operation, accessory drive belt condition and tension, radiator air flow and the fan drive operation.
WARNING: Do not remove radiator cap when engine is hot, personal injury can result.
If vehicle has been run recently, wait 15 minutes before removing the radiator cap. Place a rag over the cap and turn it to the first safety stop. Allow pressure to escape through the overflow tube. When the system pressure stabilizes, remove the cap completely.
MAXIMUM HEATER OUTPUT
Engine coolant is delivered to the heater core through two heater hoses. With the engine idling at normal operating temperature, set the temperature control to the full hot position, the mode control to the floor position, and the blower motor control to the highest speed position. Using a test thermometer, check the temperature of the air being discharged at the front floor outlets. Compare the test thermometer reading to the Heater Temperature Reference chart.
| Ambient Air Temperature |
16° C (60° F) |
21° C (70° F) |
26° C (80° F) |
32° C (90° F) |
| Minimum Air Temperature at Floor Outlet |
52° C (125° F) |
56° C (133° F) |
59° C (139° F) |
62° C (144° F) |
If the heater outlet air temperature is below the minimum specification, refer to Group 7 - Cooling. Both of the heater hoses should be hot to the touch. The coolant return heater hose should be slightly cooler than the coolant supply heater hose. If the return hose is much cooler than the supply hose, locate and repair the engine coolant flow obstruction in the cooling system. Refer to Group 7 - Cooling for more information.
OBSTRUCTED COOLANT FLOW
Possible locations or causes of obstructed coolant flow are as follows:
- Inoperative water pump.
- Inoperative thermostat.
- Pinched or kinked heater hoses.
- Improper heater hose routing.
- Plugged heater hoses or supply and return ports at the cooling system connections.
- Plugged heater core.
If proper coolant flow through the cooling system is verified, and heater outlet air temperature is low, a mechanical problem may exist.
MECHANICAL PROBLEMS
Possible causes of insufficient heat due to mechanical problems are as follows:
- Obstructed cowl air intake.
- Obstructed heater system outlets.
- Inoperative engine thermostat.
- Inoperative blower motor system.
- Inoperative A/C-heater control.
- Inoperative blend door actuator.
- Inoperative, obstructed or improperly installed blend-air door.
TEMPERATURE CONTROL
If the heater outlet air temperature cannot be adjusted with the temperature control on the A/C-heater control, the following could require service:
- Inoperative A/C-heater control.
- Inoperative blend door actuator.
- Inoperative, obstructed or improperly installed blend-air door.
- Inoperative related wiring harness or connectors.
- Improper engine coolant temperature.