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.
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The A/C compressor relay output is disabled if the ECT is above 124°C (255°F). The Check Gages indicator will illuminate at this temperature and the driver information center (DIC) will display the ENG HOT message.
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These actions will enable the A/C compressor to operate.
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This test ensures that there is sufficient refrigerant in the A/C system. The specific values come from the A/C System Performance Test.
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If an audible click is heard when the 10-amp is installed then the answer is yes.
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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.
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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.
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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.
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If the off blower motor control circuit is shorted to ground, the output of the HVAC control module 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 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 Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
Does the DIC display the ENG HOT message? | -- | Go to Engine Overheating | Go to Step 3 | |
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Important: For air conditioning (A/C) compressor operation, the evaporator core temperature must be above 0°C (32°F).
Does the A/C compressor clutch engage? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 4 | |
4 |
Does the scan tool indicate that the A/C Request Signal parameter displays Yes? | -- | Go to Step 5 | Go to Step 11 |
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 | |
6 |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 18 |
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 | |
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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.
Does the A/C compressor engage? | -- | Go to Step 9 | Go to Step 11 | |
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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.
Does the resistance value stay within the specified value range even after compressor engagement? | Temperature Minimum 14.9°C (58.82°F) - Resistance Minimum 15894 ohms Temperature Maximum 30.1°C (86.18°F) - Resistance Maximum 8024 ohms | Go to Step 25 | Go to Step 10 | |
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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.
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 15894 ohms Temperature Maximum 30.1°C (86.18°F) - Resistance Maximum 8024 ohms | Go to Step 25 | Go to Step 26 | |
11 |
Important: Access the evaporator temperature sensor control circuits and module through the glove box.
Does the DMM indicate at least the specified value? | 12 V | Go to Step 12 | Go to Step 15 |
12 |
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 Wiring Repairs . 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 Wiring Repairs . 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 Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 30 | Go to Step 16 |
Test the off blower motor control circuit of the HVAC control module for a short to ground. Refer to Circuit Testing and Wiring Repairs . 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 Wiring Repairs . 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 . Did you complete the repair? | -- | Go to Step 30 | -- |
19 | Inspect for poor connections at the A/C compressor clutch relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . 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 Connector Repairs . 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 Connector Repairs . 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 Connector Repairs . 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 Connector Repairs . Did you find and correct the condition? | -- | Go to Step 30 | Go to Step 29 |
24 | Replace the A/C compressor clutch relay. Refer to Compressor Relay Replacement . Did you complete the replacement? | -- | Go to Step 30 | -- |
25 | 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 . Did you complete the replacement? | -- | Go to Step 30 | -- |
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 . Did you complete the replacement? | -- | Go to Step 30 | -- |
27 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 30 | -- |
28 | Replace the A/C compressor. Refer to Air Conditioning Compressor Replacement . Did you complete the replacement? | -- | Go to Step 30 | -- |
29 | Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 30 | -- |
30 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2 |
