For 1990-2009 cars

### Circuit Description

When the heater and A/C controls are in any position that enables the A/C compressor, and the A/C compressor refrigerant switch is closed, the A/C request circuit is connected to B+. The engine control module (ECM) energizes the A/C compressor control circuit when a high signal voltage is detected on the A/C request circuit. The ECM will de-energize the A/C compressor control circuit during the wide open throttle (WOT) maneuvers, when the engine coolant temperature (ECT) exceeds a predetermined threshold or when the A/C request circuit signal voltage goes low, either by a pressure switch opening, or the HVAC system is in a non-A/C mode.

The ECM also receives an input on the A/C load signal circuit. This is accomplished through a pressure switch connected to B+ which is normally open. When the refrigerant high side pressure reaches approximately 1,200 kPa (174 psi), the switch closes sending a B+ signal to the ECM. The ECM will then raise the idle speed by approximately 50 RPM in order to help compensate for these conditions.

The ignition voltage is supplied directly to the A/C compressor control relay coil. The ECM controls the relay by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the component being controlled. When the ECM is commanding a component ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. The relay controls the high current flow to the A/C compressor clutch. This allows the ECM driver only to have to handle the relatively low current used by the relay.

### Conditions for Running the DTC

• | The battery voltage is between 7.5-15 volts.

• | The engine speed is more than 40 RPM.

• | The A/C clutch has been requested.

### Conditions for Setting the DTC

ECM internal circuitry determines there is an open or a short in the A/C compressor relay control circuit.

### Action Taken When the DTC Sets

The ECM will not illuminate the malfunction indicator lamp (MIL).

### Conditions for Clearing the DTC

• | The diagnostic trouble code (DTC) clears after 40 consecutive warm-up cycles in which no failures are reported by this diagnostic or any other non-emission related diagnostic.

• | The scan tool clears the DTC.

### Diagnostic Aids

If condition not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. Listen for an audible click when the A/C compressor relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

2. Tests for voltage at the coil side of the A/C compressor relay. The HEATER BLOWER fuse supplies power to the coil side of the A/C compressor relay.

3. Verifies that the ECM is providing ground to the A/C compressor relay.

4. Tests if ground is constantly being applied to the A/C compressor relay.

5. Tests if there is an internal ground in the heater and A/C controls.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: HVAC Schematics
1 | Did you perform the HVAC Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check - HVAC Systems - Automatic
2 | Important: The ambient air temperature must be above 3 degrees Celsius (38 degrees Fahrenheit).

1. Turn OFF the ignition.
2. Inspect the A/C compressor for free rotation operation.
3. Start the engine.
4. Place the HVAC control module in the OFF position.

Does the A/C compressor operate?

Go to HVAC Compressor Clutch Does Not Disengage

Go to Step 3

3 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With a scan tool, command the A/C compressor relay ON and OFF.

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

Go to Diagnostic Aids

Go to Step 4

4 |

1. Turn OFF the ignition.
2. Disconnect the A/C compressor relay.
3. Turn ON the ignition, with the engine OFF.
4. Probe the battery positive voltage circuit of the A/C compressor relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 14

5 |

1. Connect a test lamp between the control circuit of the A/C compressor relay and the battery positive voltage circuit of the A/C compressor relay.
2. With a scan tool, command the A/C compressor relay ON and OFF .

Does the test lamp turn ON and OFF with each command?

Go to Step 10

Go to Step 6

6 | Does the test lamp remain illuminated with each command? | Go to Step 8 | Go to Step 7
7 | Test the control circuit of the A/C compressor relay and the A/C cut out input of the heater and A/C controls for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 16 | Go to Step 11
8 | Disconnect the heater and A/C controls. Does the test lamp remain illuminated with each command? | Go to Step 9 | Go to Step 12
9 | Test the control circuit of the A/C compressor relay and the A/C cut out input of the heater and A/C controls for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 11
10 | Inspect for poor connections at the A/C compressor relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 13
11 | Inspect for poor connections at the harness connector of the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 15
12 | Inspect for poor connections at the harness connector of the heater and A/C controls. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 16
13 | Repair the battery positive voltage circuit of the A/C compressor relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 17 | --
14 | Replace the A/C compressor relay. Refer to Compressor Relay Replacement in Heating, Ventilation and Air Conditioning. Did you complete the replacement? | Go to Step 17 | --
15 | Important: Perform the set up procedure for the ECM . Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls-3.0L. Did you complete the replacement? | Go to Step 17 | --
16 | Important: Perform the recalibration procedure for the heater and A/C controls. Replace the heater and A/C controls. Refer to HVAC Control Module Replacement . Did you complete the replacement? | Go to Step 17 | --
17 |

1. Use the scan tool in order to clear the DTCs .
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 3

System OK