T117_F: Detect RPM Motor Failure
Status
Motor RPM failure is not a critical fault per say. However, the furnace will lose constant airflow functionality.
Description
The RPM signal from the motor has not been detected for more than 20 seconds while the motor is being commanded to run.
Expected Operation
If the RPM signal is not detected and the fault becomes active, the control shall run the blower in constant torque mode instead of constant airflow mode. In such a case, the airflow from the registers may feel more or less than normal.
Cause
There could be multiple reasons causing this failure:
1. Broken RPM cable between the motor and the furnace control.
2. Bad blower motor.
3. Broken PWM cable between the furnace control and the motor.
4. Bad furnace control board.
5. No power to the blower motor control module.
6. No line voltage to the blower motor.
Solution
Depending on the cause of failure, you may need to:
1. Use new wire harness to ensure blower gets line voltage, blower control module gets power and the RPM/PWM cables are not broken.
2. Replace blower motor.
3. Replace furnace control.
