Chevrolet Silverado / GMC Sierra. Service manual — part 2352

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
clutch should engage and disengage.

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
open/high resistance.

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
open/high resistance. If the circuit tests normal, replace the ECM/PCM.

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.
Refer to Checking Aftermarket Accessories .

Inspect the easily accessible or visible system components for obvious damage or conditions
which could cause the symptom.

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
Temperature Description and Operation.

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
Testing for Intermittent Conditions and Poor Connections .

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the
symptom:

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
Voltage

1

1

-

-

Ignition 1

1

1

-

-

A/C Low Pressure Switch Signal

1

1

1

-

A/C Compressor Clutch Relay
Control

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
circuit. This input will request the ECM to ground the A/C compressor clutch relay control
circuit, which will switch the A/C CMPRSR CLUTCH relay on. 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 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
1. A/C Compressor Inoperative

2008 Chevrolet Silverado 1500

2008 HVAC HVAC - Manual - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado