Diagnostic Instructions
Circuit/System Description
When the A/C switch is pressed, the HVAC control assembly sends a serial data message to the engine control module (ECM) for an A/C request. This input will request the ECM to ground the A/C compressor clutch relay control circuit, which will switch the
A/C CLTCH relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch assembly.
Diagnostic Aids
The following conditions must be met in order for the ECM to turn on the compressor clutch:
| • | Battery voltage is between 9-18 volts. |
| • | Engine coolant temperature (ECT) is less than 123°C (253°F). |
| • | Engine speed is less than 4,760 RPM. |
| • | Engine speed is more than 600 RPM. |
| • | A/C high side pressure is between 3102-193 kPa (450-28 psi). |
| • | Throttle position is less than 100 percent. |
| • | Evaporator temperature is greater than 2°C (35°F). |
| • | Ambient air temperature is greater than 2°C (35°F). |
| • | ECM does not detect excessive torque load. |
| • | ECM does not detect insufficient idle quality. |
Reference Information
Schematic Reference
HVAC Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Automatic HVAC Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
- Ignition OFF, disconnect the A/C relay.
- Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 and ground.
| ⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
- Verify that a test lamp illuminates between the ignition circuit terminal 85 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. |
- Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground.
| ⇒ | If the test lamp does not illuminate, test the B+ 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. |
- Disconnect the harness connector at the A/C clutch coil.
- Test for less than 1 ohm between the ground circuit terminal 2 and ground.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
- Connect the harness connector at the A/C clutch coil.
- Connect a 10-amp fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87. Verify the A/C clutch is activated.
| ⇒ | If the A/C clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the A/C clutch. |
- Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
- 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. |
- If all circuits test normal, test or replace the A/C clutch relay.
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
