GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Sonoma Pickup - 2WD 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 HVAC Compressor Clutch Does Not Engage

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).

  1. The HVAC control module is inoperative when the module does not respond to any operator control requests.

    2.

  2. Ensure to test both A/C request signal circuits of the A/C high pressure sensor for the listed conditions.

Step

Action

Yes

No

Schematic Reference:

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 perform the HVAC Diagnostic System Check?

Go to Step 2

Go to

2

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

Does the scan tool indicate that the ECT parameter is below 121°C (250°F)?

Go to Step 3

Go to

3

Important: For A/C compressor operation, 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 operate?

Go to 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. If the A/C system was operating, then allow the A/C system to equalize for approximately 2 minutes.
  4. Turn OFF the ignition.
  5. Install the ACR 2000.
  6. Record the ambient temperature at the vehicle.
  7. Record readings of the low and high side STATIC pressures.
  8. Compare the low and high side pressure values with the allowable limits for the recorded ambient air temperature. Refer to in Heating, Ventilation, and Air Conditioning.

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 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 A/C high side pressure on the scan tool to the high side pressure on the ACR 2000.

Are the high side pressure values within 103 kPa (15 psi) of each other?

Go to Step 6

Go to Step 21

6

Is the HVAC control module inoperative?

Go to Step 20

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 A/C request switch in the ON position.

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

Go to Step 10

Go to Step 8

8

Does the A/C request indicator illuminate?

Go to Step 9

Go to Step 34

9
  1. Turn OFF the ignition.
  2. Disconnect the A/C high pressure switch.
  3. Connect a 3-amp fused jumper wire between the A/C request circuits at the A/C high pressure switch connector.
  4. Start the engine.
  5. With a scan tool, observe the A/C Request Signal parameter.
  6. Place the A/C request switch in the ON position.

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

Go to Step 30

Go to Step 27

10

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

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

Go to Step 12

Go to Step 11

11
  1. Turn OFF the ignition.
  2. Disconnect the A/C low pressure switch.
  3. Connect a 3-amp fused jumper wire between the A/C low pressure switch signal and ground circuits.
  4. Start the engine.
  5. With a scan tool, observe the A/C Compressor Cycling Switch parameter.

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

Go to Step 32

Go to Step 23

12

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

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

Go to Step 16

Go to Step 13

13
  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 voltage supply 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 14

Go to Step 29

14
  1. Connect a test lamp between the control circuit of the A/C compressor clutch relay and the coil side voltage supply circuit of the A/C compressor clutch relay.
  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 31

Go to Step 15

15

Does the test lamp remain illuminated with each command?

Go to Step 19

Go to Step 18

16
  1. Turn OFF the ignition.
  2. Disconnect the A/C compressor clutch relay.
  3. Probe the switch side voltage supply 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 17

Go to Step 28

17
  1. Connect a 10 amp fused jumper wire between the switch side voltage circuit of the A/C compressor clutch relay and the A/C compressor clutch supply voltage circuit of the A/C compressor clutch.
  2. Turn ON the ignition, with the engine OFF.

Does the A/C compressor clutch engage?

Go to Step 31

Go to Step 25

18

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

Did you find and correct the condition?

Go to Step 42

Go to Step 35

19

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

Did you find and correct the condition?

Go to Step 42

Go to Step 35

20

Test the ignition 3 voltage circuit of the HVAC control module for a short to ground, a high resistance, or an open. Refer to and in Wiring Systems.

Did you find and correct the condition?

Go to Step 42

Go to Step 22

21

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

Did you find and correct the condition?

Go to Step 42

Go to Step 30

22

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

Did you find and correct the condition?

Go to Step 42

Go to Step 34

23

Test the A/C low pressure switch signal circuit for a high resistance or an open. Refer to and in Wiring Systems.

Did you find and correct the condition?

Go to Step 42

Go to Step 24

24

Test the ground circuit of the A/C low pressure switch for a high resistance or an open. Refer to and in Wiring Systems.

Did you find and correct the condition?

Go to Step 42

Go to Step 35

25

Test the A/C compressor clutch supply voltage circuit at the A/C compressor clutch for a short to ground, a high resistance, or an open. Refer to and in Wiring Systems.

Did you find and correct the condition?

Go to Step 42

Go to Step 26

26

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

Did you find and correct the condition?

Go to Step 42

Go to Step 33

27

  1. Turn OFF the ignition.
  2. Reconnect the A/C high pressure switch.
  3. Test both of the A/C request signal circuits for a short to ground, a high resistance, or an open. Refer to and in Wiring Systems.

Did you find and correct the condition?

Go to Step 42

Go to Step 35

28

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

Did you complete the repair?

Go to Step 42

--

29

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

Did you complete the repair?

Go to Step 42

--

30

Inspect for poor connections at the harness connector of the A/C high pressure sensor. Refer to and in Wiring Systems.

Did you find and correct the condition?

Go to Step 42

Go to Step 36

31

Inspect for poor connections at the A/C compressor clutch relay. Refer to and in Wiring Systems.

Did you find and correct the condition?

Go to Step 42

Go to Step 37

32

Inspect for poor connections at the harness connector of the A/C low pressure switch. Refer to and in Wiring Systems.

Did you find and correct the condition?

Go to Step 42

Go to Step 38

33

Inspect for poor connections at the harness connector of the A/C compressor clutch. Refer to and in Wiring Systems.

Did you find and correct the condition?

Go to Step 42

Go to Step 39

34

Inspect for poor connections at the harness connector of the HVAC control module. Refer to and in Wiring Systems.

Did you find and correct the condition?

Go to Step 42

Go to Step 40

35

Inspect for poor connections at the harness connector of the powertrain control module (PCM). Refer to and in Wiring Systems.

Did you find and correct the condition?

Go to Step 42

Go to Step 41

36

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

Did you complete the replacement?

Go to Step 42

--

37

Replace the A/C compressor clutch relay.

Did you complete the replacement?

Go to Step 42

--

38

Replace the A/C low pressure switch. Refer to in Heating, Ventilation, and Air Conditioning.

Did you complete the replacement?

Go to Step 42

--

39

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

Did you complete the replacement?

Go to Step 42

--

40

Important: Perform the recalibration procedure for the HVAC control module.

Replace the HVAC control module. Refer to .

Did you complete the replacement?

Go to Step 42

--

41

Important:  Perform the reprogramming procedure for the PCM.

Replace the PCM. Refer to in Engine Controls - 4.3L.

Did you complete the replacement?

Go to Step 42

--

42

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 4