Blower motor over or under voltage, or over temperature on power module

What is going on

I see this one on jobs where the power to the house is flaky or the furnace sits in a hot spot. The motor shuts itself down when line voltage is too high or too low, or when the power module overheats. Check what the furnace is actually getting before blaming the motor.

Likely causes

• High AC line voltage to the furnace
• Low AC line voltage to the furnace, often from a loose supply connection or a weak circuit
• High ambient temperatures around the furnace

Check in this order

1. Check power to the furnace and verify line voltage is within the range on the furnace rating plate.
2. Check voltage while the blower is trying to run. Low voltage that only shows under load points to a bad connection.
3. Check the installation location requirements for ambient temperature.
4. Turn power off before repair.
5. Replace the motor with the correct replacement part if needed.
6. Have a licensed electrician check the supply circuit if the voltage is out of range.

More furnace guides

• Airflow lower than demanded, furnace runs on low stage when high stage is expected
• Alternate combustion air opening (upflow or horizontal)
• Alternate vent/flue location (upflow or horizontal left)
• Annual inspection checklist
• Auxiliary limit control (location and purpose)
• Auxiliary limit switch open (blower compartment)