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Makes 🢒 GMC_Truck 🢒 2000 🢒 Yukon - 2WD 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 Blower Motor Low and Medium Speeds Inoperative

Blower Motor Low and Medium Speeds Inoperative Front

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

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

    2.

  2. This step determines if there is battery positive voltage at the blower motor resistor assembly.

    3.

  3. This step tests for voltage in each blower motor control circuit.

    4.

  4. This step tests for an open in the blower motor resistor assembly.

Step

Action

Yes

No

Schematic Reference: HVAC Blower Control Schematics

1

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

Go to Step 2

Go to Symptoms

2

  1. Turn ON the ignition, with the engine OFF.
  2. Position mode selector to the vent position.
  3. Place the blower motor switch in each speed position.

Does the blower motor operate in each speed position?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the blower motor resistor assembly connector C1.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the battery positive voltage circuit of the blower motor resistor assembly and a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 6

4

Important: Ensure the blower motor switch is in the correct speed position for the blower motor control circuit being tested.

  1. Turn OFF the ignition.
  2. Disconnect the blower motor resistor assembly connector C1.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe each blower motor control circuit with a test lamp that is connected to a known good ground.
  5. Place the blower motor switch in the appropriate speed position for the blower motor control circuit being tested.

Does the test lamp illuminate in each speed position?

Go to Step 5

Go to Step 7

5

  1. Turn OFF the ignition.
  2. Connect the blower motor resistor assembly connector C1.
  3. Disconnect the blower motor.
  4. Turn ON the ignition, with the engine OFF.
  5. Probe the blower motor voltage circuit of the blower motor with a test lamp that is connected to a good ground.
  6. Place the blower motor switch in each speed position.

Does the test lamp illuminate in each speed position?

Go to Step 8

Go to Step 9

6

Repair the battery positive voltage circuit to the blower motor resistor assembly for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in wiring systems.

Did you find and correct the condition?

Go to Step 11

--

7

Test the appropriate blower motor control circuit for an open. Refer to Circuit Testing and Wiring Repairs in wiring systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 10

8

Replace the blower motor. Refer to Blower Motor and Fan Replacement .

Did you complete the replacement?

Go to Step 11

--

9

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

Did you complete the replacement?

Go to Step 11

--

10

Replace the HVAC control module. Refer to Control Assembly Replacement .

Did you complete the replacement?

Go to Step 11

--

11

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2

Blower Motor Low and Medium Speeds Inoperative Auxiliary

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

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

    2.

  2. If the auxiliary blower motor operates correctly from the rear auxiliary HVAC control assembly, the auxiliary blower motor and auxiliary blower motor resistor assembly are functioning properly.

  3. This step tests for an open in one of the blower motor speed control circuits and determines if the auxiliary blower motor and auxiliary blower motor resistor are functioning correctly.

Step

Action

Yes

No

Schematic Reference: HVAC Blower Control Schematics

DEFINITION: The auxiliary blower motor operates in at least one speed from either the front or rear auxiliary HVAC control assembly.

1

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

Go to Step 2

Go to Symptoms

2

Important: The rear auxiliary HVAC control assembly will only function if the front auxiliary blower motor switch is placed in the REAR position.

  1. Turn ON the ignition, with the engine OFF.
  2. Operate the auxiliary blower motor in each speed position from both the front and rear auxiliary HVAC control assemblies.

Does the auxiliary blower motor operate correctly in each speed position from both the front and rear auxiliary HVAC control assemblies?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

  1. Set the front auxiliary blower motor switch to enable the rear auxiliary HVAC control assembly.
  2. Place the rear auxiliary blower motor switch in each speed position.

Does the auxiliary blower motor operate in each speed position?

Go to Step 8

Go to Step 4

4

Place the front auxiliary blower motor switch in each speed position.

Does the auxiliary blower motor operate in each speed position?

Go to Step 9

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Disconnect the auxiliary blower motor connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the auxiliary blower motor supply circuit and the auxiliary blower motor ground circuit.
  5. Place the auxiliary blower motor switch in each speed position.

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

Go to Step 17

Go to Step 6

6

Important: The auxiliary blower motor switch must be in the correct position for the auxiliary 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 blower motor resistor assembly connector C1.
  3. Probe each auxiliary blower motor speed control circuit with a test lamp that is connected to battery positive voltage.
  4. Place the front auxiliary blower motor switch in each speed position for the auxiliary blower motor speed control circuit being tested.

Does the test lamp illuminate in each position?

Go to Step 18

Go to Step 7

7

Test the appropriate auxiliary blower motor speed control circuit for an open or high resistance between the auxiliary blower motor resistor assembly and the rear auxiliary HVAC control assembly. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 24

Go to Step 14

8

Test the each auxiliary blower motor speed control circuit for an open or high resistance between the front auxiliary HVAC control assembly and the rear auxiliary HVAC control assembly. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 24

Go to Step 15

9
  1. Turn OFF the ignition.
  2. Disconnect the front auxiliary HVAC control assembly.
  3. Turn ON the ignition, with the engine OFF.
  4. Place the rear auxiliary blower motor switch in the maximum speed position.
  5. Connect a 3 amp fused jumper wire between the auxiliary HVAC switch supply voltage circuit (CKT 1923) and the front auxiliary HVAC control assembly ground circuit.

Does the auxiliary blower motor operate?

Go to Step 15

Go to Step 10

10

Is the vehicle equipped with auxiliary heat and A/C?

Go to Step 12

Go to Step 11

11

Test the auxiliary HVAC switch supply voltage circuit (CKT 1923) for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 24

Go to Step 14

12
  1. Turn OFF the ignition.
  2. Disconnect the auxiliary HVAC control processor.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a 3 amp fused jumper wire between CKT 778 and the auxiliary HVAC control processor ground circuit.

Does the auxiliary blower motor operate?

Go to Step 16

Go to Step 13

13

Test CKT 778 for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 24

Go to Step 14

14

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

Did you find and correct the condition?

Go to Step 24

Go to Step 19

15

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

Did you find and correct the condition?

Go to Step 24

Go to Step 22

16

Inspect for poor connections at the harness connector of the auxiliary HVAC control processor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 24

Go to Step 23

17

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 in Wiring Systems.

Did you find and correct the condition?

Go to Step 24

Go to Step 20

18

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

Did you find and correct the condition?

Go to Step 24

Go to Step 21

19

Replace the rear auxiliary HVAC control assembly. Refer to Control Assembly Replacement - Auxiliary .

Did you complete the replacement?

Go to Step 24

--

20

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

Did you complete the replacement?

Go to Step 24

--

21

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

Did you complete the replacement?

Go to Step 24

--

22

Replace the front auxiliary HVAC control assembly. Refer to Control Assembly Replacement - Auxiliary .

Did you complete the replacement?

Go to Step 24

--

23

Replace the auxiliary HVAC control processor.

Did you complete the replacement?

Go to Step 24

--

24

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2