Ignition voltage is supplied directly to the A/C compressor clutch relay. The engine control module (ECM) controls the relay by grounding the A/C clutch relay control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, a DTC will set.

The ECM detects an open on the control circuit of the A/C compressor clutch relay when commanded OFF with the engine in crank or run status.

The ECM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

Schematic Reference

HVAC Schematics

Connector End View Reference

HVAC Connector End Views

Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Ignition OFF, disconnect the A/C Compressor Clutch Relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay control circuit switch supply voltage terminal and relay control circuit switch control terminal and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the ignition circuit, relay coil voltage supply circuit terminal and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or a open/high resistance. If the circuit tests normal and ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary.

4. Verify that a test lamp illuminates between the relay coil B+  supply circuit, terminal, and ground.

⇒	If the test lamp does not illuminate, test the B+  supply circuit for a short to ground or a open/high resistance. If the circuit tests normal and B+ circuit fuse is open, replace the A/C Clutch Relay.

5. Disconnect the harness connector at the A/C Clutch Coil.
6. Test for less than 1.0 ohm of resistance between the A/C Clutch Coil ground circuit terminal and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the A/C Clutch Coil.
8. Connect a 3-amp fused jumper wire between the B+ supply circuit switch side terminal and control circuit switch side terminal of the A/C Clutch Relay. Verify the A/C Clutch Relay is activated.

⇒	If the A/C Clutch Relay does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the A/C Clutch Relay.

9. Connect a test lamp between the coil side of the A/C Clutch Relay ignition circuit terminal, and the control circuit terminal.
10. Command the A/C Relay output function ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM.

11. If all circuits test normal, replace the A/C Clutch Relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.