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

Test Description

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

  1. This step checks for continuous operation of the blower motor.

    2.

  2. This step tests for a short to voltage in the mode switch output and the LO, M1, M2, and HI blower motor control circuits. It is easiest to perform this step by disconnecting the blower motor resistor assembly connector, and probing each speed control circuit with a test lamp connected to a known good ground.

Step

Action

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: The blower motor is ON while the mode switch in the OFF position.

1

Did you review the HVAC operation and perform the necessary inspections?

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

2

Important: The mode switch must remain in the OFF position during this diagnostic procedure.

  1. Turn ON the ignition, with the engine OFF.
  2. Place the mode switch in the OFF position.

Is the blower motor OFF?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the blower motor resistor assembly connector.
  3. Turn the ignition ON, with the engine OFF.
  4. Probe each blower motor control circuit with a test lamp that is connected to a known good ground.

Does the test lamp illuminate on any blower motor control circuit?

Go to Step 4

Go to Step 5

4

Test the blower motor switch supply voltage circuit and the suspect blower motor control circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 9

Go to Step 6

5

Inspect for poor connections at the harness connector of the 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 9

Go to Step 7

6

Inspect for poor connections at the harness connector of the HVAC control assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 9

Go to Step 8

7

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

Did you complete the replacement?

Go to Step 9

--

8

Replace the HVAC control assembly. Refer to Heater and Air Conditioning Control Replacement .

Did you complete the replacement?

Go to Step 9

--

9

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2