For 1990-2009 cars

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
DEFINITION: A/C compressor clutch will not engage when an A/C request has been made and no Powertrain DTC are set.
1 | Did you perform the entire HVAC diagnostic system check? | -- | Go to Step 2 | Go to Diagnostic System Check
2 |

1. Turn the ignition switch to the OFF position.
2. Install both the high and low A/C freon pressure gages.
3. Read the freon pressure with the engine off.

• | Freon pressure in the high and low sides should equal each other after the A/C system has come to rest.

• | Freon pressure will fluctuate depending on ambient temperature.

• | Proper clutch operation depends on correct refrigerant charge, low freon charge will shut off A/C compressor operation.

Is the high and low side freon pressures below the specified value?

345 kPa (50 psi)

Go to Leak Testing

Go to Step 3

3 | Is the high and low side freon pressures above the specified value? | 690 kPa (100 psi) | Go to Step 4 | Go to Step 5
4 | Evacuate and recharge the A/C system according to proper freon fill specifications. Has the A/C system been recharged properly? | -- | Go to Step 24 | --
5 | Test for a short to ground in CKT 59. Refer to Circuit Testing in Wiring Systems. Is a short present? | -- | Go to Step 6 | Go to Step 7
6 | Repair a short to ground in CKT 59 between the underhood accessory wiring junction block and the A/C compressor clutch coil. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 24 | --
7 |

1. Remove the A/C CLU relay from the underhood accessory wiring junction block.
2. Disconnect the A/C compressor clutch coil connector. Refer to Air Conditioning Clutch Coil Removal in HVAC - Heating, Ventilation, and Air Conditioning.
3. Connect a 10A fused jumper between the ignition feed terminal for the switch side of the A/C CLU relay and underhood accessory wiring junction block connector C1 terminal F8.
4. Connect a DMM between the A/C compressor clutch coil connector terminal B and ground. Refer to Circuit Testing in Wiring Systems.
5. Turn the ignition switch to the RUN position.
6. Measure the available voltage at the A/C compressor clutch coil connector terminal B.

Is the voltage within the specified values?

B+

Go to Step 9

Go to Step 8

8 | Repair a poor connection or an open in CKT 59. Refer to Wiring Repairs or Connector Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 24 | --
9 | Using a DMM, measure for continuity between terminal B of the A/C compressor clutch coil connector and ground. Refer to Circuit Testing in Wiring Systems. Is the resistance to ground less than the specified value? | 0-2ohms | Go to Step 11 | Go to Step 10
10 | Repair a poor connection or an open in circuit 1050. Refer to Wiring Repairs or Connector Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 24 | --
11 |

1. Disconnect the Powertrain Control Module (PCM) connector C2.
2. Reinstall the A/C CLU relay.
3. Connect a 10A fused jumper between the PCM connector C2 terminal 39 and ground.
4. Turn the ignition switch to the RUN position.
5. Using a DMM, measure the voltage between the A/C compressor clutch coil connector terminal B and ground. Refer to Circuit Testing in Wiring Systems.

Is the voltage within the specified values?

B+

Go to Step 12

Go to Step 13

12 |

1. Remove the fused jumper from the PCM connector C2 terminal 39 and ground.
2. Reconnect the A/C compressor clutch coil connector. Refer to Air Conditioning Clutch Coil Installation in HVAC - Heating, Ventilation, and Air Conditioning.
3. Reinstall the fused jumper between the PCM connector C2 terminal 39 and ground.
4. Turn the ignition on.

Does the A/C compressor clutch engage?

--

Go to Cooling Insufficient - Air Conditioning (A/C) System

Go to Step 23

13 |

1. Turn the ignition switch to the OFF position.
2. Remove the A/C CLU relay.
3. Using a DMM, measure for continuity between the PCM connector C2 terminal 39 and the underhood accessory wiring junction block connector C1 terminal F7. Refer to Circuit Testing in Wiring Systems.

Is there continuity?

0-2ohms

Go to Step 15

Go to Step 14

14 | Repair a poor connection or an open in CKT 459. Refer to Wiring Repairs or Connector Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 24 | --
15 | Replace the A/C CLU relay and retest the A/C system. Refer to Compressor Relay Replacement . Does replacing the A/C CLU relay correct the concern? | -- | Go to Step 24 | Go to Step 16
16 |

1. Disconnect the heater-A/C control connector C2.
2. Connect a DMM between the PCM connector C2 terminal 22 and the heater-A/C control connector C2 terminal B. Refer to Circuit Testing in Wiring Systems.
3. Measure CKT 762 for resistance between these two connectors.

Is CKT 762 resistance between the specified values?

0-2ohms

Go to Step 18

Go to Step 17

17 | Repair a poor connection or an open in CKT 762. Refer to Wiring Repairs or Connector Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 24 | --
18 |

1. Connect a DMM, between the PCM connector C2 terminal 22 and ground. Refer to Circuit Testing in Wiring Systems.
2. Measure CKT 762 for continuity to ground.

Is CKT 762 continuous to ground?

--

Go to Step 19

Go to Step 20

19 | Repair a short to ground in CKT 762. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 24 | --
20 |

1. Disconnect the DMM.
2. Reconnect all connectors back to their respective modules.
3. Install the scan tool to the diagnostic link connector.
4. Start the engine and allow it to idle in park.
5. Select the area of the scan tool which will read HVAC button output status.
6. Depress the A/C button on/off several times.

Does the scan tool read the A/C request being sent by the HVAC control head?

--

Go to Step 21

Go to Step 22

21 |

1. Inspect the connections between the PCM and the underhood accessory wiring junction block.

Important: Perform the reprogramming procedure for the PCM.

2. If OK, replace the PCM. Refer to Powertrain Control Module Replacement/Programming in Engine Controls.

Is the repair complete?

--

Go to Step 24

--

22 | Replace the heater-A/C control. Refer to HVAC Module Assembly Replacement . Is the repair complete? | -- | Go to Step 24 | --
23 | Replace the A/C compressor clutch coil. Refer to Air Conditioning Clutch Coil Replacement . Is the repair complete? | -- | Go to Step 24 | --
24 |

1. Turn the ignition switch to the OFF position.
2. Reconnect all connectors/components disconnected.

Have all repairs been made?

--

Go to Diagnostic System Check

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