GM Service Manual Online
For 1990-2009 cars only

Diagnostic Aids

The air conditioning (A/C) compressor clutch will not engage under the following conditions:

    • The A/C high side line pressure is over 2 413 kPa (350 psi).
    • Throttle angle is at 100 percent.
    • Engine speed is more than 5,500 RPM.
    • Engine coolant temperature (ECT) is more than 123°C (253°F).
    • Evaporator core temperature is less than 0°C (32°F).
    • The powertrain control module (PCM) minimum OFF time to engage the compressor is 7-9 seconds. The scan tool, A/C Relay Command Delay, body control module (BCM) Inputs data list, can validate this.
    • The evaporator temperature sensor is normally closed. The evaporator temperature sensor opens at 0°C (32°F).

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 124°C (255°F). The check gages indicator will illuminate at this temperature and the DIC will display the ENG HOT message.

  2. These actions will enable the A/C compressor to operate.

  3. This test ensures that there is sufficient refrigerant in the A/C system. The specific values come from the A/C System Performance Test in Heating, Ventilation and Air Conditioning.

  4. If an audible click is heard when the 10-amp fused jumper is installed then the answer is yes.

  5. Checks the function of the thermistor of the evaporator temperature sensor. The thermistor and module side of the harness are located behind the glove box.

  6. Checks the resistance of the two gray wires at the evaporator temperature sensor module behind the glove box. As the evaporator gets colder the evaporator circuit resistance goes up.

  7. Checks the resistance of the two gray wires running out of the evaporator temperature sensor itself located at the evaporator core which is contained within the HVAC module or HEBA. As the evaporator gets colder the evaporator circuit resistance goes up.

  8. If the Off blower motor control circuit is shorted to ground, the output of the HVAC control assembly for an A/C request is disabled.

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: The air conditioning (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?

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Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Manual

2

  1. Start the engine.
  2. Observe the driver information center (DIC) message center.

Does the DIC display the ENG HOT message?

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Go to Engine Overheating in Engine Cooling

Go to Step 3

3

Important: For the air conditioning (A/C) compressor operation, the evaporator core temperature must be above 0°C (32°F).

  1. Start the engine.
  2. Place the blower motor switch in the low speed position.
  3. Place the A/C request switch to the ON position.

Does the A/C compressor clutch engage?

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

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the A/C Request Signal parameter in the body control module (BCM) inputs data list.
  4. Place the A/C request switch to the ON position.

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

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Go to Step 5

Go to Step 11

5

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

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

Above 16°C (60°F) 345 kPa (50 psi)

Above 24°C (75°F) 483 kPa (70 psi)

Above 33°C (90°F) 690 kPa (100 psi)

Go to Step 6

Go to Leak Testing in Heating, Ventilation and Air Conditioning

6

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

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 18

7

Connect a 10-amp fused jumper between the battery positive voltage circuit and 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 19

Go to Step 13

8

Important: Access the evaporator temperature sensor gray control circuits and module with three way connector to BCM and HVAC control module behind the glove box.

  1. Disconnect the evaporator temperature sensor at the 3-wire connector running from the evaporator temperature control circuits to the HVAC control module and BCM behind the glove box.
  2. Connect a test light between the A/C request circuit of the HVAC control module and the BCM at the 3-wire connector of the evaporator temperature sensor.

Does the A/C compressor engage?

--

Go to Step 9

Go to Step 11

9

Important: Access the evaporator temperature sensor gray control circuits and module with three way connector to BCM and HVAC control module behind the glove box.

  1. With a 3-amp fused jumper attached between the BCM and the HVAC control module A/C request circuits at the 3-wire evaporator temperature sensor behind the glove box.
  2. Check the resistance of the two gray evaporator temperature sensor circuits at the evaporator temperature sensor behind the glove box.
  3. Start the engine.

Does the resistance value stay within the specified value range even after compressor engagement?

Temperature Minimum 14.9°C (58.82°F) - Resistance Minimum 15651 ohms

Temperature Maximum 30.1°C (86.18°F) - Resistance Maximum 8190 ohms

Go to Step 25

Go to Step 10

10

Important: Access the evaporator temperature sensor gray control circuits and module with three way connector to BCM and HVAC control module behind the glove box.

  1. With a 3-amp fused jumper attached between the BCM and the HVAC control module A/C request circuits at the 3-wire evaporator temperature sensor behind the glove box.
  2. Cut the two gray evaporator temperature sensor circuits no less than 2 inches from the evaporator temperature sensor module behind the glove box.
  3. Start the engine.
  4. Check the resistance of the two gray wires at the evaporator temperature sensor coming out of the evaporator core at the HVAC module.

Does the resistance value move from the specified value range when the compressor is engaged?

Temperature Minimum 14.9°C (58.82°F) - Resistance Minimum 15651 ohms

Temperature Maximum 30.1°C (86.18°F) - Resistance Maximum 8190 ohms

Go to Step 25

Go to Step 26

11

Important: Access the evaporator temperature sensor gray control circuits and module with three way connector to BCM and HVAC control module behind the glove box.

  1. Disconnect the evaporator temperature sensor at the 3-wire pinout running to the HVAC control module behind the glove box.
  2. Probe the A/C request signal circuit of the HVAC control module with a DMM connected to a good ground.

Does the DMM indicate at least the specified value?

12 V

Go to Step 12

Go to Step 15

12

  1. Connect a 3-amp fused jumper between the A/C request signal circuit of the HVAC control module and the A/C request signal circuit of the BCM.
  2. Observe the A/C Request Signal parameter.

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

--

Go to Step 20

Go to Step 17

13

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

Did you find and correct the condition?

--

Go to Step 30

Go to Step 14

14

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

Did you find and correct the condition?

--

Go to Step 30

Go to Step 23

15

Test the A/C request signal circuit of the HVAC control module for a short to ground, a high resistance and for an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 30

Go to Step 16

16

Test the Off blower motor control circuit of the HVAC control module for 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 30

Go to Step 23

17

Test the A/C request signal circuit of the BCM for a short to ground, a high resistance and for an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 30

Go to Step 21

18

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

Did you complete the repair?

--

Go to Step 30

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19

Inspect for poor connections at 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 30

Go to Step 20

20

Inspect for poor connections at the evaporator temperature sensor control circuits at the evaporator control module behind the glove box. 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 30

Go to Step 25

21

Inspect for poor connections at the BCM. 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 30

Go to Step 27

22

Inspect for poor connections at the A/C compressor clutch. 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 30

Go to Step 28

23

Inspect for poor connections at the HVAC control module. 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 30

Go to Step 29

24

Replace the A/C compressor clutch relay.

Did you complete the replacement?

--

Go to Step 30

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25

Replace the evaporator temperature sensor control side circuits of the harness. This includes the module with the 3-way connector side of the harness located behind the glove box. Refer to Evaporator Temperature Sensor Replacement in Heating, Ventilation and Air Conditioning.

Did you complete the replacement?

--

Go to Step 30

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26

Replace the evaporator temperature sensor whole harness. This includes from the harness circuits and components at the sensor in the evaporator core to the evaporator control module side of the harness located behind the glove box. Refer to Evaporator Temperature Sensor Replacement in Heating Ventilation, and Air Conditioning.

Did you complete the replacement?

--

Go to Step 30

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27

Important: Program the BCM.

Replace the BCM. Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

--

Go to Step 30

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28

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

Did you complete the replacement?

--

Go to Step 30

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29

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

Did you complete the replacement?

--

Go to Step 30

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30

Operate the system in order to verify the repair.

Did you correct the condition?

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System OK

Go to Step 2