Circuit Description
The air conditioning (A/C) compressor clutch relay is controlled by the engine control module (ECM). Ignition 1 voltage is supplied directly to the A/C compressor clutch relay. The ECM controls the relay by grounding the 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. Each 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 sets.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P0646 Air Conditioning (A/C) Clutch Relay Control Circuit Low Voltage |
| • | DTC P0647 Air Conditioning (A/C) Clutch Relay Control Circuit High Voltage |
Conditions for Running the DTC
| • | The engine is running. |
| • | The ignition 1 voltage is more than 11 volts. |
| • | The A/C is requested ON. |
| • | The A/C compressor is running (P0647 only) |
| • | The DTC runs continuously once the above conditions are met. |
Conditions for Setting the DTC
The ECM detects a low voltage on the A/C clutch relay control circuit for more than 25 seconds.
OR
The ECM detects a high voltage on the A/C clutch relay control circuit for more than 25 seconds.
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
| • | For HVAC system concerns, refer to HVAC Preliminary Checks . |
| • | If condition is intermittent refer to Testing for Intermittent Conditions and Poor Connections . |
| • | The following table illustrates the A/C clutch relay terminal locations in the underhood fuse block: |
A/C Clutch Relay Terminal Identification | |
|---|---|
B+ - Switch | Control |
Ignition 1 Voltage - Coil | A/C Compressor Clutch |
Front of Vehicle | |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: HVAC Schematics Connector End View Reference: Component Connector End Views | |||||||||
1 |
Important: This diagnostic trouble code (DTC) will only set for a failure on the control side of the A/C Clutch Relay. Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |||||||
Does the A/C Relay turn ON and OFF? | Go to Step 3 | Go to Step 4 | |||||||
3 |
Did the DTC fail this ignition? | Go to Step 4 | Go to Diagnostic Aids | ||||||
4 |
Does the test lamp illuminate? | Go to Step 5 | Go to Step 9 | ||||||
5 |
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 A/C clutch relay control circuit for the following:
Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 14 | Go to Step 11 | ||||||
8 | Test the A/C clutch relay control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 14 | Go to Step 11 | ||||||
9 |
Did you complete the repair? | Go to Step 14 | -- | ||||||
10 | Test for an intermittent and for a poor connection at the A/C clutch relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 14 | Go to Step 12 | ||||||
11 | Test for an intermittent and for a poor connection at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 14 | Go to Step 13 | ||||||
12 | Replace the A/C clutch relay. Refer to Relay Replacement . Did you complete the replacement? | Go to Step 14 | -- | ||||||
13 | Replace the ECM. Did you complete the replacement? | Go to Step 14 | -- | ||||||
14 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 15 | ||||||
15 | Observe the capture info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |||||||
