Blower Motor Malfunction
Blower Motor Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
The HVAC control assembly 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:
* Low speed-3 resistors
* Medium 1 speed-2 resistors
* Medium 2 speed-1 resistor
When the operator requests High speed, the HVAC control assembly applies voltage to the blower motor through the high blower motor resistor assembly.
Diagnostic Aids
Be sure the blower motor housing is not shorted to a grounded surface causing the blower motor to run continuously at high speed.
Circuit/System Verification
Ignition ON, mode selector set to Heat, command the blower motor from LOW through HIGH by changing the blower motor switch from LOW through to the HIGH speed positions, the blower motor should operate from low to high when changing between the commanded states.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the blower motor resistor assembly.
2. Test for less than 1.0 ohm between the ground circuit terminal C and ground.
^ If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal A and ground.
^ If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, replace the blower motor resistor assembly.
4. Mode selector set to Heat, while changing the fan speed switch between LOW, M1, M2 and HIGH, verify that a test lamp illuminates between ground and the appropriate blower motor control circuit terminals listed below:
* LOW terminal E
* M1 terminal D
* M2 terminal F
* HIGH terminal B
^ 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 and the ignition circuit fuse is open, replace the HVAC control assembly.
5. Ignition OFF, connect the harness connector at the blower motor resistor assembly and disconnect the harness connector at the blower motor.
6. Test for less than 1.0 ohm between the ground circuit terminal A and ground.
^ If greater than the specified range, replace the blower motor resistor assembly.
7. Ignition ON, mode selector set to Heat, connect a test lamp between the control circuit terminal B and ground circuit terminal A.
8. Cycle the fan speed switch between LOW, M1, M2 and HIGH speeds. The test lamp should illuminate and change in intensity as the blower speed is varied.
^ If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the blower motor resistor assembly.
^ If the test lamp does not change intensity, test the control circuit for a short to voltage. If the circuit tests normal, replace the blower motor resistor assembly.
9. If all circuits test normal, test or replace the blower motor.
Component Testing
1. Ignition OFF, disconnect the harness connector at the blower motor.
2. Install a 40-amp fused jumper wire between the control circuit terminal B and 12 volts. Install a jumper wire between the ground circuit terminal A and ground. Verify the blower motor activates.
^ If the blower motor does not activate, replace the blower motor.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
Blower Motor Replacement
Refer to Programming and Relearning. Programming and Relearning