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The ECM detects an open on the control circuit of the A/C compressor clutch relay when Action Taken When the DTC Sets The ECM will store conditions which were present when the DTC set as Failure Records data Conditions for Clearing the DTC A history DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction. Reference Information Schematic Reference HVAC Schematics Connector End View Reference Component Connector End Views Description and Operation Air Delivery Description and Operation Air Temperature Description and Operation Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Scan Tool Reference Control Module References for scan tool information Circuit/System Verification Ignition ON, command the A/C Relay ON and OFF with a scan tool. Feel/listen for the A/C relay
2008 Chevrolet Silverado 1500 2008 HVAC HVAC - Manual - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
Circuit/System Testing 1. Ignition OFF, disconnect the A/C relay. 2. 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. 3. 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 4. 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 5. Disconnect the harness connector at the A/C clutch coil. 6. 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. 7. Connect the harness connector at the A/C clutch coil. 8. 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. 9. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86. 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 If the test lamp is always OFF, test the control circuit for a short to voltage, or an 11. If all circuits test normal, test or replace the A/C clutch relay. Component Testing 1. Ignition OFF, disconnect the A/C COMP relay. 2. Test for 60-180 ohms between terminals 85 and 86.
2008 Chevrolet Silverado 1500 2008 HVAC HVAC - Manual - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
If the resistance is not within the specified range, replace the relay. 3. Test for infinite resistance between the following terminals: 30 and 86 30 and 87 30 and 85 85 and 87 If not the specified value, replace the relay. 4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 If greater than the specified range, replace the relay. Repair Procedures Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Relay Replacement (Attached to Wire Harness) or Relay Replacement (Within an Control Module References for ECM replacement, setup, and programming DTC P0646 OR P0647 Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provides an overview of each diagnostic category. DTC Descriptors DTC P0646 Air Conditioning (A/C) Clutch Relay Control Circuit Low Voltage DTC P0647 Air Conditioning (A/C) Clutch Relay Control Circuit High Voltage Diagnostic Fault Information
2008 Chevrolet Silverado 1500 2008 HVAC HVAC - Manual - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
Circuit/System Description The engine control module (ECM)/powertrain control module (PCM) controls the A/C B+ is applied to the A/C relay in the RUN/START position and with the A/C compressor clutch Conditions for Running the DTC An A/C request is received from the HVAC module. Conditions for Setting the DTC A short to voltage, short to ground, or open/high resistance is seen on the A/C compressor clutch Action Taken When the DTC Sets DTC P0646 and DTC P0647 are Type C DTCs Conditions for Clearing the DTC DTC P0646 and DTC P0647 are Type C DTCs Reference Information Schematic Reference HVAC Schematics Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance A/C Relay Coil B+ P0646 P0647 P0647 - A/C Compressor Clutch Relay P0646 P0647 P0647 -
2008 Chevrolet Silverado 1500 2008 HVAC HVAC - Manual - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
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