For 1990-2009 cars

Refer to

#### A/C Compressor Clutch Relay, A/C Compressor Clutch

Engine Controls Components
Air Conditioning (A/C) Compressor Clutch Control Diagnosis
Cooling Fan Relay, Cooling Fan Motor
Brake Switch and Automatic Transaxle
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

When A/C is selected through the A/C control head a 12 volt signal is supplied to the A/C request input of the PCM. The A/C compressor clutch relay is controlled through the PCM. The PCM monitors the A/C refrigerant pressure. If the A/C refrigerant pressure, and engine operating conditions are within a specific calibrated acceptable ranges the PCM will enable the A/C compressor relay. This is accomplished by providing a ground path for the A/C relay coil within the PCM. When the A/C compressor relay is enabled battery voltage is supplied to the compressor clutch coil.

The PCM will enable the A/C compressor clutch whenever the engine is running and the A/C has been requested, unless any of the following conditions are met:

• | Throttle greater than 90%

• | A/C head pressure greater than 414 psi (4.27 volts) or less than 34 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor).

• | Ignition voltage below 10.5 volts.

• | Engine speed greater than 4500 RPM for 5 seconds or 5400 RPM.

• | ECT greater than 125°C (257°F).

• | IAT less than 5°C (41°F)

### Test Description

The numbers below refer to numbers on the Diagnostic Table.

The A/C compressor clutch should not be engaged with the engine running if an A/C mode is not selected at the control head.

1. Stored Diagnostic Trouble Codes (That may not illuminate the Malfunction indicator Lamp) may disable the A/C compressor. This Diagnostic Table may lead to improper diagnosis and replacement of good parts if Diagnostic Trouble Codes are present.

2. The A/C compressor clutch should apply if the conditions under the Notice have been met.

3. Checks for an A/C request signal from the control head to the PCM.

4. Checks the ignition feed circuit to the A/C relay.

5. Determines whether the A/C relay or the circuitry is at fault.

6. Determines whether or not the PCM is turning the A/C relay ON due to a false A/C request.

7. Isolates problem to the A/C control head or the PCM.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain OBD System Check
2 | Are any PCM DTC(s) stored? | -- | Go to applicable DTC table(s) | Go to Step 3
3 | Important: The following conditions must be met before continuing with this step:

• | Ambient air temperature must be above 5°C (41°F).

• | A/C Pressure must be above 36°C (96°F).

• | Coolant temperature must be below 121°C (250°F).

1. A/C selector switch OFF.
2. Ignition ON, engine OFF.
3. Listen for engagement of the A/C clutch.

Is the A/C Clutch engage.

--

Go to Step 18

Go to Step 4

4 |

1. Start engine.
2. Select Defrost or MAX mode on HVAC control head.
3. Observe A/C compressor.

Is the A/C compressor clutch engaged?

--

Go to Diagnostic Aids

Go to Step 5

5 | With Defrost or Max mode selected, monitor A/C Request display on the scan tool Engine data list. Does A/C Request display Yes? | -- | Go to Step 9 | Go to Step 6
6 |

1. Ignition OFF, disconnect the PCM.
2. Ignition ON.
3. With Defrost or Max mode selected, measure voltage on the A/C request circuit at the PCM harness connector.

Does the voltage measure near the specified value?

B+

Go to Step 8

Go to Step 7

7 |

1. Check the A/C request circuit for the following conditions:

• | Open;

• | Shorted to ground;

• | Poor connection at the A/C control head or A/C programmer (as applicable).

2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 29

Go to Electrical Diagnosis for A/C Controls diagnostics

8 |

1. Check the A/C request circuit for a poor connection at the PCM.
2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 29

Go to Step 27

9 | Observe A/C refrigerant pressure display on the scan tool. Is indicated A/C pressure between the specified values? | 36 - 440 psi | Go to Step 12 | Go to Step 10
10 |

1. Connect J 39183-C R-134a Manifold gauge set. Refer to Heater, Ventilation and Air Conditioning.
2. Observe high side refrigerant pressure on the gauge.

Is high side refrigerant pressure within the specified values?

36 - 440 psi

Go to Step 11

Go to Refrigerant Recovery and Recharging Procedures in Heater, Ventilation and Air Conditioning

11 |

1. Ignition OFF, disconnect A/C Pressure sensor.
2. Ignition ON.
3. View A/C Highside display on the scan tool Engine data list.

Does the scan tool display an A/C Highside pressure at the specified value?

0 psi

Go to Step 28

Go to Step 27

12 |

1. Disconnect the A/C relay electrical connector.
2. Probe the ignition feed circuits at the A/C relay harness connector with a test light to ground.

Is the test light ON?

--

Go to Step 13

Go to Step 23

13 | Connect a fused jumper between the ignition feed circuit and A/C compressor clutch control circuit at the A/C relay connector. Does the A/C compressor clutch engage? | -- | Go to Step 14 | Go to Step 15
14 |

1. Check for poor connections at A/C relay.
2. If a problem is found, replace faulty terminals as necessary. Refer to Engine Electrical.

Was a problem found?

--

Go to Step 29

Go to Step 24

15 |

1. Disconnect the A/C compressor clutch electrical connector (leave the ignition control circuit and A/C compressor clutch control circuit jumpered at the A/C relay connector).
2. Connect a test light between A/C compressor clutch feed circuit and the compressor ground circuit.

Is the test light ON?

--

Go to Step 16

Go to Step 17

16 |

1. Check for poor connections at the A/C compressor clutch.
2. If a problem is found, replace faulty terminals as necessary.

Was a problem found?

--

Go to Step 29

Go to Step 25

17 |

1. Check for an open or short to ground in the A/C compressor clutch control circuit.
2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 29

Go to Step 26

18 |

1. Ignition ON
2. A/C OFF
3. Observe A/C Request display on the scan tool.

Does A/C Request display Yes?

--

Go to Step 19

Go to Step 21

19 |

1. Ignition OFF.
2. Disconnect the PCM.
3. Ignition ON, A/C OFF.
4. Using a DVM, measure voltage between the A/C request circuit at the PCM harness connector and ground.

Does the voltage measure near the specified value?

B+

Go to Step 20

Go to Step 27

20 |

1. Ignition OFF, disconnect the A/C control head.
2. Ignition ON, check the A/C Request circuit for a short to B+.

If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 29

Go to Electrical Diagnosis for A/C Controls diagnostics

21 |

1. Disconnect A/C relay.
2. Start vehicle and observe the A/C compressor.

Is the A/C compressor clutch engaged?

--

Go to Step 22

Go to Step 24

22 | Locate and repair short to voltage in the A/C compressor clutch control circuit (CKT 59). Is action complete? | -- | Go to Step 29 | --
23 | Repair open or short to ground in ignition feed circuit to the A/C compressor relay. Is action complete? | -- | Go to Step 29 | --
24 | Replace A/C compressor relay. Is action complete? | -- | Go to Step 29 | --
25 | Repair A/C compressor clutch. Refer to V6 Air Conditioning Compressor Service. Is action complete? | -- | Go to Step 29 | --
26 | Locate and repair open in A/C compressor clutch ground circuit (CKT 450). Is action complete? | -- | Go to Step 29 | --
27 | Replace the PCM. Important: The replacement PCM must be programmed. Refer to PCM Replacement/Programming . Is action complete? | -- | Go to Step 29 | --
28 | Replace A/C refrigerant pressure sensor. Is action complete? | -- | Go to Step 29 | --
29 | Important: The following conditions must be met before continuing with this step:

• | Ambient air temperature must be above 5°C (41°F).

• | A/C Pressure must be above 36°C (96°F).

• | Coolant temperature must be below 121°C (250°F).

1. Ignition ON, engine running.
2. Turn A/C selector switch ON.
3. Listen for engagement of the A/C clutch.

Is the A/C Clutch engage.

--

System OK

Go to Step 3