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Connector End View Reference Component Connector End Views Description and Operation Air Temperature Description and Operation Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References for scan tool information. Circuit/System Verification Engine running, command the A/C Relay On and OFF with a scan tool. The A/C compressor Circuit/System Testing 1. Ignition OFF, disconnect the A/C relay. 2. Ignition ON, verify a test lamp illuminates between the relay coil B+ circuit terminal and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an 3. Connect a test lamp between the relay coil B+ circuit terminal and the A/C compressor clutch relay control circuit terminal. 4. Engine running, command the A/C relay ON and OFF. 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
2008 Chevrolet Silverado 1500 2008 HVAC HVAC - Manual - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
circuit tests normal, replace the ECM/PCM. If the test lamp is always OFF, test the control circuit for a short to voltage or an 5. If all circuits test normal, test or replace the A/C relay. Repair Procedures Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Control Module References for ECM/PCM replacement, setup, and programming SYMPTOMS - HVAC SYSTEMS - MANUAL Visual/Physical Inspection Inspect for aftermarket devices which could affect the operation of the HVAC System. Inspect the easily accessible or visible system components for obvious damage or conditions Verify the A/C compressor clutch turns freely and is not seized. The A/C compressor will not operate in cold outside air temperatures. Refer to Air The following could cause window fogging: Wet carpet or mats High humidity Interior water leak Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves Inspect the air distribution system for causes of reduced air flow: Obstructed or dirty passenger compartment air filter, if equipped IMPORTANT: Review the system operation in order to familiarize yourself with the system functions. Refer to the following procedures: Air Delivery Description and Operation Air Temperature Description and Operation
2008 Chevrolet Silverado 1500 2008 HVAC HVAC - Manual - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
Blocked or damaged air inlet or outlet vents Intermittent Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Symptom List Refer to a symptom diagnostic procedure from the following list in order to diagnose the Blower Motor Malfunction Air Conditioning Compressor Malfunction Noise Diagnosis - Air Conditioning (A/C) System Noise Diagnosis - Blower Motor Odor Diagnosis AIR CONDITIONING COMPRESSOR MALFUNCTION 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. Diagnostic Fault Information Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance B+ 1 1 - - A/C Relay Coil Side Supply 1 1 - - Ignition 1 1 1 - - A/C Low Pressure Switch Signal 1 1 1 - A/C Compressor Clutch Relay P0645 P0645 P0645 - A/C Relay Coil Side Ground - 1 - - A/C Low Pressure Switch - 1 - -
2008 Chevrolet Silverado 1500 2008 HVAC HVAC - Manual - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
Circuit/System Description When the A/C switch is pressed, the HVAC control module grounds the A/C request signal 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 greater than 600 RPM Engine speed is less than 4,760 RPM A/C high side pressure is between 2929-269 kPa (39-425 psi) Throttle position is less than 100 percent Evaporator temperature is greater than 0°C (32°F) ECM does not detect excessive torque load ECM does not detect insufficient idle quality The ambient temperature is above 1°C (34°F) Reference Information Schematic Reference HVAC Schematics Connector End View Reference Component Connector End Views Description and Operation Air Temperature Description and Operation Air Delivery Description and Operation Ground
2008 Chevrolet Silverado 1500 2008 HVAC HVAC - Manual - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
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