The HVAC control module applies voltage 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:

When the operator requests High speed, the HVAC control module applies voltage to the blower motor relay through the high blower motor control circuit. The voltage energizes the blower motor relay, connecting the blower motor to the high blower motor control circuit.

Be sure the blower motor housing is not shorted to a grounded surface causing the blower motor to run continuously at high speed.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for Scan Tool Information

Listen to the function of the blower motor while commanding the blower motor speed from Off through to the High speed positions using the blower motor switch, the blower motor should turn ON and the speed should vary from Low through High.

Blower Motor Inoperative

1. Ignition OFF, disconnect the RUN RLY relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the B+ circuit terminal and ground.

⇒	If the test lamp does not illuminate, test the B+, ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal for a short to ground. If the circuit tests normal, test or replace the RUN RLY relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Ignition OFF, disconnect the harness connector X3 at the HVAC control module.
6. Connect a test lamp between the control circuit terminal G and ground.
7. Ignition ON, connect a 25A fused jumper wire between the B+ circuit terminal and the control circuit terminal. Verify the test lamp illuminates.

⇒	If the test lamp does not illuminate, test the control circuit for an open/high resistance.

8. Connect a test lamp between the B+ circuit terminal and the control circuit terminal.
9. Command the run relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

10. If all circuits test normal, test or replace the RUN RLY relay.
11. Ignition OFF, connect the RUN RLY relay.
12. Connect the harness connector X3 at the HVAC control module and disconnect the harness connector at the blower motor resistor assembly.
13. Ignition ON, set the front blower motor switch to the 1 position and verify that a test lamp illuminates between the blower motor control circuit terminal B and ground.

⇒	If the test lamp does not illuminate, replace the HVAC control module.

14. Ignition OFF, connect the harness connector at the blower motor resistor assembly and disconnect the blower motor.
15. Test for less than 1.0 ohm of resistance between the bower motor ground circuit terminal B and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance, if the circuit tests normal, replace the blower motor resistor assembly.

16. Ignition ON, connect a test lamp between the blower motor control circuit terminal and ground.
17. Cycle the fan speed switch between the 1, 2, 3, 4 and 5 positions. The test lamp should illuminate and change in intensity as the blower speed is varied.

⇒	If the test lamp is always OFF or does not change intensity, replace the blower motor resistor assembly.

18. If all circuits test normal, test or replace the blower motor.

Blower Motor Malfunction

1. Ignition OFF, disconnect the harness connector at the blower motor resistor assembly.
2. Ignition ON, while changing the fan speed switch between the 1, 2, 3, 4 and 5 positions, verify that a test lamp illuminates between ground and the appropriate blower motor control circuit terminals listed below:

•	1 terminal B

•	2 terminal A

•	3 terminal D

•	4 terminal C

•	5 terminal F

⇒	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 tests normal, replace the HVAC control module.

3. Verify that a test lamp illuminates between the B+ circuit terminal G and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

4. Ignition OFF, connect the harness connector at the blower motor resistor assembly and disconnect the blower motor.
5. Ignition ON, connect a test lamp between the blower motor control circuit terminal A and the blower motor ground circuit terminal B.
6. Cycle the fan speed switch between the 1, 2, 3, 4 and 5 positions. The test lamp should illuminate and change in intensity as the blower speed is varied.

⇒	If the test lamp does not illuminate or does not change intensity, replace the blower motor resistor assembly.

7. If all circuits test normal, test or replace the blower motor.

Blower Motor Test

1. Ignition OFF, disconnect the harness connector at the blower motor.
2. Install a 40-amp fused jumper wire between the control circuit terminal A and 12 volts. Install a jumper wire between the ground circuit terminal B and ground. Verify the blower motor activates.

⇒	If the blower motor does not activate, replace the blower motor.

Relay Test

1. Ignition OFF, disconnect the RUN RLY relay.
2. Test for 60-200 ohms of resistance between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If less than infinite resistance, replace the relay.

4. Install a 3-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Measure for less than 2 ohms of resistance between terminals 30 and 87.

⇒	If greater than 2 ohms, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.