GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series (Crew) C4/C5 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 Auxiliary Blower Motor Malfunction

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step will determine if one or more blower speeds are inoperative.

    2.

  2. This step tests for a voltage change in the auxiliary heater blower motor feed circuit.

  3. This step tests for an open in one of the auxiliary heater blower motor speed control circuits and the auxiliary heater blower motor switch.

Step

Action

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: The auxiliary blower motor operates in at least one, but not all, speed positions.

1

Did you review the auxiliary heater and A/C operation and perform the necessary inspections?

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

2

  1. Turn ON the ignition, with the engine OFF.
  2. Place the auxiliary heater blower motor switch in each speed position.

Does the auxiliary heater blower motor operate in each speed position?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Disconnect the auxiliary heater blower motor connector C2.
  2. Turn ON the ignition, with the engine OFF.
  3. Test the auxiliary heater blower motor supply circuit with a test lamp to the auxiliary heater blower motor ground circuit. Refer to Circuit Testing and Wiring Repairs .
  4. Place the auxiliary heater blower motor switch in each speed position.

Does the test lamp illuminate and change intensity in each speed position?

Go to Step 7

Go to Step 4

4

Important: The auxiliary heater blower motor switch must be in the correct position for the auxiliary heater blower motor speed control circuit being tested. Failure to do this will result in a misdiagnosis.

  1. Turn OFF the ignition.
  2. Disconnect the auxiliary heater blower motor resistor assembly.
  3. Test the LO, MED and HI auxiliary heater blower motor speed control circuits with a test lamp to a known good ground. Refer to Circuit Testing .
  4. Place the auxiliary heater blower motor switch in each speed position for the auxiliary heater blower motor speed control circuit being tested.

Does the test lamp illuminate in each speed position?

Go to Step 8

Go to Step 5

5

Test the appropriate auxiliary heater blower motor speed control circuit for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 6

6

Inspect for poor connections at the harness connector of the auxiliary heater blower motor switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 9

7

Inspect for poor connections at the harness connector of the auxiliary heater blower motor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 10

8

Inspect for poor connections at the harness connector of the auxiliary heater blower motor resistor assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 12

Go to Step 11

9

Replace the auxiliary heater blower motor switch. Refer to Heater Control Blower Switch Replacement .

Did you complete the replacement?

Go to Step 12

--

10

Replace the auxiliary heater blower motor . Refer to Auxiliary Blower Motor Replacement .

Did you complete the replacement?

Go to Step 12

--

11

Replace the auxiliary heater blower motor resistor assembly. Refer to Auxiliary Blower Motor Resistor Assembly Replacement .

Did you complete the replacement?

Go to Step 12

--

12

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2