Chevrolet Silverado / GMC Sierra. Service manual — part 2353

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

1. Engine running, press the A/C request switch. The A/C compressor clutch should engage.

2. Place the mode switch in the defrost position. The A/C compressor clutch should engage.

If the clutch does not engage refer to

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the A/C low pressure switch.

2. Test for less than 5 ohms between the ground circuit terminal B and ground.

If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool Low Pressure Switch parameter is Open.

If not the specified value, test the signal circuit terminal A for a short to ground. If the
circuit tests normal, replace the HVAC control module

4. Connect a 3-amp fused jumper wire between the signal circuit terminal A and ground.

Verify the scan tool Low Pressure Switch parameter is Closed.

If not the specified value, test the signal circuit for a short to voltage or an open/high
resistance. If the circuit tests normal, replace the HVAC control module

5. Connect the harness connector at the A/C low pressure switch. Verify the scan tool Low

Pressure Switch parameter is Closed.

If not the specified value, test or replace the A/C low pressure switch.

6. Ignition OFF, disconnect the A/C relay.

7. 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.

8. Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground.

2008 Chevrolet Silverado 1500

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

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.

9. 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.

10. Disconnect the harness connector at the A/C clutch coil.

11. 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.

12. Connect the harness connector at the A/C clutch coil.

13. 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.

14. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal

86.

15. 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.

16. If all circuits test normal, test or replace the A/C clutch relay.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Air Conditioning Compressor Replacement (LY2, LY5, LH6, L76, L92 and LMG) or
Air Conditioning Compressor Replacement (LLY/LMM) or Air Conditioning
Compressor Replacement (LU3)

Compressor Clutch Plate/Hub Assembly Replacement (4.3L, 6.6L) or Compressor
Clutch Plate/Hub Assembly Replacement (V8 - Gas)

Control Module References for HVAC control module and ECM replacement, setup, and
programming

2008 Chevrolet Silverado 1500

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

BLOWER MOTOR 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/System Description

The blower motor control module is an interface between the HVAC control module and the
blower motor. The blower motor speed control, battery positive and ground circuits enable the
control module to operate. The HVAC control module provides a variable voltage to the blower
motor control module to request the selected blower speed. The blower motor control module
provides a pulse width modulation (PWM) signal to the blower motor in order to control the
blower motor speed. The module supplies 12 volts to the blower motor through the blower motor
voltage supply circuit.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Blower Motor Control
Module B+

1

1

-

-

Blower Motor B+

1

1

-

-

Blower Motor Speed Control

2

1

1

-

Blower Motor Control

2

1

1

-

Ground

-

1

-

-

1. Blower Motor Inoperative
2. Blower Motor Always On

2008 Chevrolet Silverado 1500

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

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 Testing

1. Ignition OFF, disconnect the X2 harness connector at the blower motor control module.

2. Test for less than 1.0 ohm between the ground circuit terminal 5 and ground.

If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 6 and

ground.

If the test lamp does not illuminate, test the B+ circuit for a short to ground or an
open/high resistance. If the circuit tests normal and the B+ circuit fuse (HVAC BLWR
40-amp) in the underhood fuse block is open, test all components connected to the B+
circuit and replace as necessary.

4. Connect a DMM between the control circuit terminal 3 and ground.

5. Cycle the blower motor from OFF to HIGH. The voltage should increase while changing

between the commanded states.

If voltage remains greater than 11.5 volts while changing between the commanded
states, test the control circuit for a short to voltage. If the circuit test normal, replace
the HVAC control module.

If voltage remains less than 1.0 volts while changing between the commanded states,
test the control circuit for a short to ground or an open/high resistance. If the circuit
tests normal, replace the HVAC control module.

If voltage is between 1.0-11.5 volts and does not increase when changing between the
commanded states, replace the HVAC control module.

2008 Chevrolet Silverado 1500

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