GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 Auxiliary Blower Motor Inoperative

Test Description

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

  1. This step tests for auxiliary heater blower motor operation in any speed setting.

    2.

  2. This step identifies the presence of battery positive voltage at the auxiliary heater blower motor switch.

    3.

  3. This step tests for a possible open in the A/C relay ground circuit.

Step

Action

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: The auxiliary blower motor is inoperative in all speed positions.

1

Did you review the rear Heat or 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

Connect a test lamp between the auxiliary HVAC switch supply voltage circuit and a known good ground. Refer to Circuit Testing and Wiring Repairs .

Did the test lamp illuminate?

Go to Step 8

Go to Step 4

4

Test the A/C relay coil ignition 3 circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 21

Go to Step 5

5

Test the A/C relay battery positive voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 21

Go to Step 6

6

Connect a test lamp between the A/C relay ignition-3 circuit and the ground circuit. Refer to Circuit Testing and Wiring Repairs .

Does the test lamp illuminate?

Go to Step 13

Go to Step 7

7

Repair an open in the A/C relay ground circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 21

--

8
  1. Turn the ignition OFF.
  2. Disconnect the auxiliary blower motor.
  3. Connect a test lamp between the blower motor supply voltage and a known good ground. Refer to Circuit Testing and Wiring Repairs .
  4. Place the auxiliary blower motor switch from the minimum speed position to the maximum speed position.

Does the test lamp illuminate and change intensity for each position?

Go to Step 9

Go to Step 11

9
  1. Turn the ignition OFF.
  2. Disconnect the auxiliary blower motor.
  3. Turn the ignition ON with the engine OFF.
  4. Connect a test lamp between the blower motor supply voltage and the blower motor ground circuit. Refer to Circuit Testing and Wiring Repairs .
  5. Place the auxiliary blower motor switch from the minimum speed position to the maximum speed position.

Does the test lamp illuminate and change intensity for each position?

Go to Step 16

Go to Step 10

10

Test the blower motor ground circuit for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 21

--

11

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

  1. Turn OFF the ignition.
  2. Connect the auxiliary blower motor.
  3. Disconnect the auxiliary blower motor resistor assembly.
  4. Turn the ignition ON with the engine OFF.
  5. Test the auxiliary blower motor high, medium and low speed circuits with a test lamp connected to a good ground. Refer to Circuit Testing and Wiring Repairs .
  6. Place the auxiliary blower motor switch in the appropriate speed position for each circuit being tested.

Does the test lamp illuminate for each speed position?

Go to Step 15

Go to Step 12

12

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

Did you find and correct the condition?

Go to Step 21

Go to Step 14

13

Inspect for poor connections at the harness connector of the A/C relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 21

Go to Step 17

14

Inspect for poor connections at the harness connector of the auxiliary 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 21

Go to Step 18

15

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

Did you find and correct the condition?

Go to Step 21

Go to Step 19

16

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

Did you find and correct the condition?

Go to Step 21

Go to Step 20

17

Replace the A/C relay.

Did you complete the replacement?

Go to Step 21

--

18

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

Did you complete the replacement?

Go to Step 21

--

19

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

Did you complete the replacement?

Go to Step 21

--

20

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

Did you complete the replacement?

Go to Step 21

--

21

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2