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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2005 🢒 Aztek - AWD 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 HVAC Compressor Clutch Does Not Engage

Diagnostic Aids

The Mitsubishi scroll type A/C compressor carries an internal thermal cut off switch. The thermal cut off switch normal operation is to open and disable the compressor under extreme load and temperatures above 155°C (311°F). The internal thermal cut off switch is non-serviceable.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. The A/C compressor relay output is disabled if engine coolant temperature is above 121°C (250°F). The engine coolant indicator will illuminate at this temperature.

  1. Place the mode switch in any position except OFF, and place the air temperature control switch in a cold setting. Use the bi-level mode for consistent testing of the A/C system operation.

    2.

  2. The HVAC control module is inoperative if the module does not respond to any operator control requests.

    3.

  3. The evaporator temperature sensor is replaced as part of the evaporator core.

Step

Action

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: The A/C compressor clutch will not engage if an A/C request has been made, and a powertrain DTC has not been set.

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Start the engine.
  2. Observe the coolant temperature indicator.

Is the engine coolant temperature indicator illuminated?

Go to Engine Coolant Temperature Indicator Always On in Engine Cooling

Go to Step 3

3

Important: For A/C compressor operation, the ambient air temperature must be above 3°C (38°F).

  1. Start the engine.
  2. Place the blower motor switch in the maximum speed position.
  3. Place the A/C request switch in the ON position.
  4. Place the air temperature switch in the coldest position.

Does the A/C compressor clutch engage?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 4

4
  1. Park the vehicle inside or out of direct sunlight.
  2. Open the window in order to ventilate the interior of the vehicle.
  3. If the A/C system was operating, then wait for approximately 2 minutes.
  4. Turn OFF the ignition.
  5. Install the J 43600 ACR 2000 Air Conditioning Service Center.
  6. Record the ambient air temperature at the vehicle.
  7. Record readings of the low and high side STATIC pressures.
  8. Compare the low side pressure values and the high side pressure values with the allowable limits for the recorded ambient air temperature. Refer to Air Conditioning (A/C) System Performance Test.

Are the pressure values within the allowable limits for the recorded ambient air temperature, and within 103 kPa (15 psi) of each other?

Go to Step 5

Go to Leak Testing in Heating, Ventilation and Air Conditioning

5
  1. Turn ON the ignition, with the engine OFF.
  2. With a scan tool, observe the A/C High Side pressure sensor parameter in the powertrain data list.
  3. Compare the pressure values with the specifications for the ambient air temperature.

Are the pressure values within specifications for the ambient air temperature, and within 103 kPa (15 psi) of each other?

Go to Step 6

Go to Step 27

6

Is the HVAC control module inoperative?

Go to Step 19

Go to Step 7

7
  1. Start the engine.
  2. With a scan tool, observe the A/C request signal parameter in the Powertrain data list.
  3. Place the air temperature switch in the coldest position.
  4. Place the A/C request switch in the ON position.

Does the scan tool indicate that the A/C request signal parameter is YES?

Go to Step 14

Go to Step 8

8
  1. Start the engine.
  2. With a scan tool, observe the A/C switch parameter in the Body Control Module (BCM) data list.
  3. Place the air temperature switch in the coldest position.
  4. Place the A/C request switch in the ON position.

Does the scan tool indicate that the A/C switch parameter is Active?

Go to Step 22

Go to Step 9

9

Does the A/C request indicator illuminate?

Go to Step 10

Go to Step 31

10
  1. Turn OFF the ignition.
  2. Test the A/C request signal circuit for the following:
    3. • A short to voltage
    •  A high resistance
    • An open

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 11

11
  1. Disconnect the evaporator temperature sensor.
  2. Measure the resistance of the evaporator temperature sensor. Refer to Sensor Resistance Table.

Is the resistance measurement near the values specified in the sensor resistance table?

Go to Step 12

Go to Step 34

12

Test the evaporator temperature signal circuit for the following:

    • A short to ground
    • A high resistance
    • An open

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 13

13

Test the low reference circuit for the following:

    • A short to ground
    • A high resistance
    • An open

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 36

14

With a scan tool, command the A/C compressor clutch relay ON and OFF.

Does the clutch relay turn ON and OFF with each command?

Go to Step 18

Go to Step 15

15
  1. Turn OFF the ignition.
  2. Disconnect the A/C compressor clutch relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the coil side of the voltage supply circuit with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 16

Go to Step 30

16
  1. Connect a test lamp between the control circuit and the coil side of the voltage supply circuit.
  2. With a scan tool, command the A/C compressor clutch relay ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 33

Go to Step 17

17

Does the test lamp remain illuminated with each command?

Go to Step 25

Go to Step 24

18
  1. Turn OFF the ignition.
  2. Disconnect the A/C compressor clutch relay.
  3. Probe the switch side of the voltage supply circuit with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 19

Go to Step 29

19
  1. Connect a 10-amp fused jumper between the switch side voltage circuit of the clutch relay and the supply voltage circuit of the clutch.
  2. Turn ON the ignition, with the engine OFF.

Does the A/C compressor clutch engage?

Go to Step 33

Go to Step 26

20

Test the ignition 3 voltage circuit of the HVAC control module for the following:

    • A short to ground
    • A high resistance
    • An open

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 21

21

Test the ground circuit of the HVAC control module for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 36

22
  1. Start the engine.
  2. Place the A/C request in the ON position.
  3. Measure the voltage on the request circuit at the BCM to a good ground.

Does the value measure near battery voltage?

Go to Step 37

Go to Step 23

23

Test the A/C request signal circuit for the following:

    • A short to ground
    • A high resistance
    • An open

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 46

Go to Step 36

24

Test the control circuit of the A/C compressor clutch relay for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 38

25

Test the control circuit of the A/C compressor clutch relay for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 38

26

Test the supply voltage circuit at the A/C compressor clutch for the following:

    • A short to ground
    • A high resistance
    • An open

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 28

27

Test the ground circuit of the A/C pressure sensor for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 32

28

Test the ground circuit of the A/C compressor clutch for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 35

29

Repair the switch side voltage supply circuit of the A/C compressor clutch relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 46

--

30

Repair the coil side of the voltage supply circuit of the A/C compressor clutch relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 46

--

31

Test the off blower motor control circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 36

32

Inspect for poor connections at the harness connector of the A/C high pressure sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairsin Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 39

33

Inspect for poor connections at the A/C compressor clutch relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 41

34

Inspect for poor connections at the harness connector of the evaporator temperature sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairsin Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 40

35

Inspect for poor connections at the harness connector of the A/C compressor clutch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairsin Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 42

36

Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 43

37

Inspect for poor connections at the harness connector of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 44

38

Inspect for poor connections at the harness connector of the powertrain control module (PCM) or engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 46

Go to Step 45

39

Replace the A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heating, Ventilation and Air Conditioning.

Did you complete the replacement?

Go to Step 46

--

40

Replace the evaporator temperature sensor. Refer to Air Conditioning Evaporator Core Replacement in Heating, Ventilation and Air Conditioning.

Did you complete the replacement?

Go to Step 46

--

41

Replace the A/C compressor clutch relay. Refer to Compressor Relay Replacement in Heating, Ventilation and Air Conditioning.

Did you complete the replacement?

Go to Step 46

--

42

Replace the A/C compressor clutch coil. Refer to Air Conditioning Compressor Replacement in Heating, Ventilation and Air Conditioning.

Did you complete the replacement?

Go to Step 46

--

43

Replace the HVAC control module. Refer to HVAC Control Module Replacement.

Did you complete the replacement?

Go to Step 46

--

44

Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 46

--

45

Replace the PCM/ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 46

--

46

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 4