GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2003 🢒 TopKick C-Series (Conventional) C6/C7/C8 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 HVAC Compressor Clutch Does Not Engage

HVAC Compressor Clutch Does Not Engage 7.8L

Test Description

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

  1. For the purpose of this and future steps where A/C operation is necessary, bi-level mode is used for consistent testing.

    2.

  2. This step ensures that there is a proper amount of refrigerant in the A/C system to be able to close the A/C pressure switches.

    3.

  3. There is two control circuits for the coil side of the A/C compressor clutch relay. The A/C compressor clutch control circuit, which provides the relay with ignition 3 voltage, is the correct circuit to test.

    4.

  4. An audible click sound will be made by the A/C compressor clutch if it engages.

    5.

  5. If the fused jumper opens during this test, the circuit or ECM input is shorted to ground.

    6.

  6. If circuit is shorted to ground, ensure to inspect the HVAC 20 ampere circuit breaker

    7.

  7. If no concern with the circuit, the engine control module (ECM) is pulling the circuit to ground. The ECM can not disable the A/C compressor relay.

    8.

  8. If the A/C fuse is open ensure to test the battery positive circuit, A/C compressor clutch supply voltage circuit, and the A/C compressor clutch coil for short to ground.

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 when an A/C request has been made and a Powertrain DTC has not been set.

1

Did you review the HVAC operation and perform the necessary inspections?

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

2

  1. Start the engine.
  2. Place the blower motor switch in the maximum speed position.
  3. Place the mode switch in the bi-level position.
  4. Place the air temperature control switch in the coldest position.

Does the A/C compressor operate?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Park the vehicle inside or in the shade.
  2. Open the windows in order to ventilate the interior of the vehicle.
  3. Turn OFF the ignition.
  4. If the A/C system was operating, allow the A/C system to equalize for about 2 minutes.
  5. Install the J 39500-B ACR 4.
  6. Record the ambient temperature at the vehicle.
  7. Record readings of the low and high side STATIC pressures.

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

Go to Step 4

Go to Leak Testing

4
  1. Start the engine.
  2. Place the mode switch to the bi-level position.
  3. With a scan tool observe the A/C Request Signal parameter in the Powertrain Engine data list.

Does the scan tool indicate that the A/C Request Signal parameter is Yes?

Go to Step 5

Go to Step 10

5

  1. Turn OFF the ignition.
  2. Disconnect the A/C compressor clutch relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Place the mode switch to the bi-level position.
  5. Probe the A/C compressor clutch control circuit of the A/C compressor clutch relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 19

6

Probe the A/C low pressure switch signal circuit of the A/C compressor clutch relay with a test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

Go to Step 7

Go to Step 12

7
  1. Disconnect the A/C compressor clutch relay.
  2. Measure the resistance of the relay coil.

Does the resistance measure near 77 ohms?

Go to Step 8

Go to Step 28

8

Probe the battery positive voltage circuit of the A/C compressor clutch relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 9

Go to Step 20

9

  1. Turn OFF the ignition.
  2. Connect a 10-amp fused jumper across the battery positive voltage circuit of the A/C compressor clutch relay to the A/C compressor clutch supply voltage circuit of the A/C compressor clutch relay.

Does the A/C compressor clutch engage?

Go to Step 22

Go to Step 14

10
  1. Turn OFF the ignition.
  2. Disconnect the A/C high pressure switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the A/C request signal circuit of the A/C high pressure switch with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 16

11

  1. Connect a 5-amp fused jumper wire between the A/C request signal circuit of the A/C high pressure switch and the A/C compressor control circuit of the A/C high pressure switch.
  2. With a scan tool observe the A/C Request Signal parameter.

Does the scan tool indicate that the A/C Request Signal parameter is Yes?

Go to Step 23

Go to Step 17

12
  1. Turn OFF the ignition.
  2. Disconnect the A/C low pressure switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ground circuit of the A/C low pressure switch with a test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

Go to Step 13

Go to Step 21

13
  1. Connect a 5-amp fused jumper wire between the A/C low pressure switch signal circuit of the A/C low pressure switch and the ground circuit of the A/C low pressure switch.
  2. Probe the A/C low pressure switch signal circuit of the A/C compressor clutch relay with a test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

Go to Step 24

Go to Step 18

14

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

    • A high resistance
    • An open

Refer to Circuit Testing and to Wiring Repairs .

Did you find and correct the condition?

Go to Step 34

Go to Step 15

15

Test the ground circuit of the A/C compressor clutch for the following conditions:

    • A high resistance
    • An open

Refer to Circuit Testing and to Wiring Repairs .

Did you find and correct the condition?

Go to Step 34

Go to Step 25

16

Test the A/C request signal circuit of the A/C high pressure switch for the following conditions:

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

Refer to Circuit Testing and to Wiring Repairs .

Did you find and correct the condition?

Go to Step 34

Go to Step 26

17

Test the A/C compressor clutch relay control circuit of the A/C high pressure switch for the following conditions:

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

Refer to Circuit Testing and to Wiring Repairs .

Did you find and correct the condition?

Go to Step 34

Go to Step 27

18

Test the A/C low pressure switch signal circuit of the A/C low pressure switch for the following conditions:

    • A high resistance
    • An open

Refer to Circuit Testing and to Wiring Repairs .

Did you find and correct the condition?

Go to Step 34

Go to Step 22

19

Repair the A/C compressor clutch control circuit. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 34

--

20

Repair the battery positive voltage circuit of the A/C compressor clutch relay. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 34

--

21

Repair the ground circuit of the A/C low pressure switch. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 34

--

22

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

Did you find and correct the condition?

Go to Step 34

Go to Step 28

23

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

Did you find and correct the condition?

Go to Step 34

Go to Step 29

24

Inspect for poor connections at the harness connector of the A/C low pressure switch. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs .

Did you find and correct the condition?

Go to Step 34

Go to Step 30

25

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

Did you find and correct the condition?

Go to Step 34

Go to Step 31

26

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

Did you find and correct the condition?

Go to Step 34

Go to Step 32

27

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

Did you find and correct the condition?

Go to Step 34

Go to Step 33

28

Replace the A/C compressor clutch relay. Refer to Compressor Relay Replacement .

Did you complete the replacement?

Go to Step 34

--

29

Replace the A/C high pressure switch. Refer to Air Conditioning (A/C) High Pressure Switch Replacement .

Did you complete the replacement?

Go to Step 34

--

30

Replace the A/C low pressure switch. Refer to Air Conditioning Cycling Switch Replacement .

Did you complete the replacement?

Go to Step 34

--

31

Replace the A/C compressor clutch coil or A/C compressor. Refer to the appropriate repair procedure:

Did you complete the replacement?

Go to Step 34

--

32

Replace the HVAC control assembly. Refer to Heater and Air Conditioning Control Replacement .

Did you complete the replacement?

Go to Step 34

--

33

Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data .

Did you complete the replacement?

Go to Step 34

--

34

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3

HVAC Compressor Clutch Does Not Engage 6.6L, 8.1L

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).

    2.

  2. For the purpose of this and future steps where A/C operation is necessary, bi-level mode is used for consistent testing.

    3.

  3. With each command, an audible click sound should be made.

    4.

  4. There is two A/C request signal circuits that connect to the A/C high pressure switch. The circuit that is to be tested is wired between the HVAC control assembly and the A/C high pressure switch.

  5. There is two A/C request signal circuits that connect to the A/C high pressure switch. The circuit that is to be tested is wired between the engine control module (ECM)/ powertrain control module (PCM) and the A/C high pressure switch.

  6. There are 2 A/C request signal circuits that connect to the A/C high pressure switch. The circuit that is to be tested is wired between the HVAC control assembly and the A/C high pressure switch.

  7. There are 2 A/C request signal circuits that connect to the A/C high pressure switch. The circuit that is to be tested is wired between the ECM/PCM and the A/C high pressure switch.

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 when an A/C request has been made and a Powertrain DTC has not been set.

1

Did you review the HVAC operation and perform the necessary inspections?

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

2

  1. Start the engine.
  2. With a scan tool, observe the ECT Sensor parameter in the Powertrain Engine data list.

Does the ECT Sensor parameter indicate a value over 121°C (250°F)?

Go to Symptoms - Engine Cooling in Engine Cooling

Go to Step   3

3

Important: For A/C compressor operation, outside 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 mode switch in the bi-level position.
  4. Place the air temperature switch in the coldest position.

Does the A/C compressor operate?

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

Go to Step 4

4
  1. Park the vehicle inside or in the shade.
  2. Open the windows in order to ventilate the interior of the vehicle.
  3. Turn OFF the ignition.
  4. If the A/C system was operating, allow the A/C system to equalize for about 2 minutes.
  5. Install the J 39500-B ACR 4.
  6. Record the ambient temperature at the vehicle.
  7. Record readings of the low and high side STATIC pressures.

Are the low and high side 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. Start the engine.
  2. With a scan tool, observe the A/C Request Signal parameter in the Powertrain Engine data list.
  3. Place the blower motor switch in the maximum speed position.
  4. Place the mode switch in the A/C position.
  5. Place the air temperature switch in the coldest position.

Does the scan tool indicate that the A/C Request Signal parameter is YES?

Go to Step 6

Go to Step 11

6

With a scan tool, observe the A/C Compressor Cycling Switch parameter in the Powertrain Engine data list.

Does the scan tool indicate that the A/C Compressor Cycling Switch parameter is YES?

Go to Step 7

Go to Step 13

7

  1. Start the engine.
  2. With a scan tool, command the A/C Relay ON and OFF.

Does the A/C compressor clutch relay turn ON and OFF with each command?

Go to Step 9

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Disconnect the A/C compressor clutch relay.
  3. Connect a test lamp between the ignition 3 voltage circuit of the A/C compressor clutch relay to the A/C compressor clutch relay control circuit of the A/C compressor clutch relay.
  4. Start the engine.
  5. With a scan tool, command the A/C Relay ON and OFF.

Does the test lamp illuminate with each command?

Go to Step 26

Go to Step 15

9

Probe the battery positive voltage circuit of the A/C compressor clutch relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 10

Go to Step 23

10
  1. Turn OFF the ignition.
  2. Connect a 10-amp fused jumper across the battery positive voltage circuit of the A/C compressor clutch relay to the A/C compressor clutch supply voltage circuit of the A/C compressor clutch relay.

Does the A/C compressor clutch engage?

Go to Step 26

Go to Step 17

11

  1. Turn OFF the engine.
  2. Disconnect the A/C high pressure switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the A/C request signal circuit of the HVAC control assembly with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 12

Go to Step 20

12

  1. Connect a 3-amp fused jumper across both of the A/C request signal circuits of the A/C high pressure switch.
  2. With a scan tool, observe the A/C Request Signal parameter in the Powertrain Engine data list.

Does the scan tool indicate that the A/C Request Signal parameter is YES?

Go to Step 27

Go to Step 21

13
  1. Turn OFF the engine.
  2. Disconnect the A/C low pressure switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ground circuit of the A/C low pressure switch with a test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

Go to Step 14

Go to Step 24

14
  1. Connect a 3-amp fused jumper across the A/C low pressure switch signal circuit of the A/C low pressure switch and the ground circuit of the A/C low pressure switch.
  2. With a scan tool, observe the A/C Compressor Cycling Switch parameter in the Powertrain Engine data list.

Does the scan tool indicate that the A/C Compressor Cycling Switch parameter is YES?

Go to Step 28

Go to Step 22

15
  1. Turn OFF the engine.
  2. Connect a test lamp between the A/C compressor clutch relay control circuit of the A/C compressor clutch relay and battery positive voltage.
  3. Start the engine.
  4. With a scan tool, command the A/C Relay ON and OFF.

Does the test lamp illuminate with each command?

Go to Step 25

Go to Step 16

16

Test the A/C compressor clutch relay control circuit of the A/C high pressure switch for the following conditions:

    • A high resistance
    • An open

Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 31

17
  1. Disconnect the A/C compressor clutch.
  2. Probe the A/C compressor clutch supply voltage circuit of the A/C compressor clutch with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 19

Go to Step 18

18

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

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

Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 29

19

Test the ground circuit of the A/C compressor clutch for the following conditions:

    • A high resistance
    • An open

Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 29

20

Test the A/C request signal circuit of the HVAC control assembly for the following conditions:

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

Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 30

21

Test the A/C request signal circuit of the ECM/PCM for the following conditions:

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

Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 31

22

Test the A/C low pressure switch signal circuit of the ECM/PCM for the following conditions:

    • A high resistance
    • An open

Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 31

23

Repair the battery positive circuit of the A/C compressor clutch relay.

Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

--

24

Repair the ground circuit of the A/C low pressure switch.

Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

--

25

Repair the ignition 3 voltage circuit of the A/C compressor clutch relay.

Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

--

26

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

Did you find and correct the condition?

Go to Step 38

Go to Step 32

27

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

Did you find and correct the condition?

Go to Step 38

Go to Step 33

28

Inspect for poor connections at the harness connector of the A/C low pressure switch. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 34

29

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

Did you find and correct the condition?

Go to Step 38

Go to Step 35

30

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

Did you find and correct the condition?

Go to Step 38

Go to Step 36

31

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

Did you find and correct the condition?

Go to Step 38

Go to Step 37

32

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 38

--

33

Replace the A/C high pressure switch. Refer to Air Conditioning (A/C) High Pressure Switch Replacement in Heating, Ventilation, and Air Conditioning.

Did you complete the replacement?

Go to Step 38

--

34

Replace the A/C low pressure switch. Refer to Air Conditioning (A/C) Low Pressure Switch Replacement in Heating, Ventilation and Air Conditioning.

Did you complete the replacement?

Go to Step 38

--

35

Replace the A/C compressor clutch coil or A/C compressor. Refer to the appropriate repair procedure:

    •  Air Conditioning Clutch Coil Replacement in Heating, Ventilation, and Air Conditioning
    •  Air Conditioning Compressor Replacement in Heating, Ventilation, and Air Conditioning

Did you complete the replacement?

Go to Step 38

--

36

Replace the HVAC control assembly. Refer to Heater and Air Conditioning Control Replacement .

Did you complete the replacement?

Go to Step 38

--

37

Replace the ECM/PCM. Refer to the appropriate procedure:

    •  Engine Control Module Replacement in Engine Controls-6.6L
    •  Powertrain Control Module Replacement in Engine Controls-8.1L

Did you complete the replacement?

Go to Step 38

--

38

Operate the system in order to verify the repair.

Did you correct the condition?

Go to Step 2

--