GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2007 🢒 H3 🢒 HVAC 🢒 HVAC - Manual 🢒 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.

Circuit/System Description

The HVAC control assembly applies a ground to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request:

    • Low speed, 3 resistors
    • Medium 1 speed, 2 resistors
    • Medium 2 speed, 1 resistors

When the operator requests High speed, the HVAC control assembly applies ground to the high speed blower relay control circuit. When the relay contacts close, ground is applied directly to the blower motor through the blower motor resistor.

Reference Information

Schematic Reference

HVAC Schematics

Description and Operation

    •  Air Temperature Description and Operation
    •  Air Delivery Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Output Controls
    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Verification
  1. Turn ON the ignition, verify that the HVAC relay turns on.
    2. ⇒If the HVAC relay does not turn on, refer to the HVAC Relay Malfunction test.
  2. Ignition On, place the blower switch in the highest speed position, the blower motor should operate at High speed.
    3. ⇒If the blower motor does not function properly in the High speed position, refer to High Speed Blower Malfunction.
  3. Place the blower switch in Low, Medium 1 and Medium 2 speed positions. The blower motor should operate in each speed position.
    4. ⇒If the blower motor does not function properly in each speed position, refer to Blower Malfunction.

Circuit/System Testing

HVAC Relay Malfunction

  1. Ignition OFF, disconnect the HVAC relay in the underhood fuse block.
  2. Test for less than 1.0 ohm of resistance between the relay coil ground circuit terminal and ground.
    3. ⇒If greater than specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify that a test lamp illuminates between the relay coil control circuit terminal and ground.
    4. ⇒If the test lamp does not illuminate, replace the underhood fuse block.
  4. If all circuits test normal, test or replace the HVAC relay.

High Speed Blower Malfunction

  1. Ignition OFF, disconnect the harness connector C1 at the HVAC Control Module.
  2. Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal 5 and ground.
    3. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect the harness connector at the HVAC Control Module.
  4. Disconnect the High Speed Blower Relay.
  5. Place the blower switch in the high speed position.
  6. Ignition OFF test for less than 1.0 ohm of resistance between the ground circuit terminal 5 and ground.
    7. ⇒If greater than the specified range, test the ground circuit for an open/high resistance. If the circuit test normal test or replace the HVAC Control Module.
  7. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 2 and ground.
    8. ⇒If the test lamp does not illuminate, test the ignition circuit for an open/high resistance.
  8. Test for less than 1.0 ohm of resistance between the ground circuit terminal 1 and ground.
    9. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  9. Connect the High Speed Blower Relay. Disconnect the harness connector at the Blower Motor Resistor.
  10. Ignition ON, place the blower switch in the high speed position.
  11. Test for less than 1.0 ohm of resistance between the control circuit terminal E at the Blower Motor resistor and ground.
    12. ⇒If greater than the specified range, test the control circuit for an open/high resistance. If the circuit test normal test or replace the High Speed Blower Relay.
  12. Ignition OFF, connect the harness connector at the Blower Motor Resistor. Connect the High Speed Blower Relay. Disconnect the harness connector at the Blower Motor.
  13. Ignition On, place the blower switch in the high speed position.
  14. Verify that a test lamp illuminates between the control circuit terminal 1 and B+.
    15. ⇒If the test lamp does not illuminate, test the control circuit for an open/high resistance.
    ⇒If the circuit test normal, test or replace the Blower Motor Resistor.
  15. Verify that a test lamp illuminates between the ignition circuit terminal 2 and ground.
    16. ⇒If the test lamp does not illuminate test the ignition circuit for an open/high resistance.
  16. If all circuits test normal, test or replace the Blower Motor.

Blower Malfunction

  1. Ignition OFF, disconnect the harness connector at the HVAC Control Module.
  2. Test for less than 1.0 ohm of resistance between the ground circuit terminal 5 and ground.
    3. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect the harness connector at the HVAC Control Module.
  4. Disconnect the harness connector at the Blower Motor Resistor.
  5. Ignition ON, place the Blower Switch in the appropriate speed for the circuit being tested.
  6. Verify that a test lamp illuminates between the appropriate control circuit and B+.
    7. ⇒If the test lamp does not illuminate, test the appropriate control circuit for a short to ground or an open/high resistance. If the circuit test normal, test or replace the HVAC control Module.
  7. If all circuits test normal, test or replace the Blower Motor Resistor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Control Module References
    •  Blower Motor Replacement
    •  Heater and Air Conditioning Control Replacement
    •  Blower Motor Resistor Assembly Replacement