General ECM blower checks

What is going on

Before you condemn an ECM blower motor, go through the basic mechanical and electrical checks. Many motors are replaced when the real problem was a loose connector, a bad thermostat call or a wheel that has slipped on the shaft. Switch off and lock out the power before you handle harnesses, wheel or motor, and let the motor sit for a few minutes, since an ECM can hold a charge. Work through each item and write down what you find.

Likely causes

• Supply voltage outside the rating plate range
• Damaged or poorly seated power or control harness
• Thermostat or wiring not sending a proper cooling, heating or continuous fan demand
• Wheel loose on shaft, broken or unbalanced
• Rubbing or binding between wheel, housing or motor

Check in this order

1. Check that the power supply is within the rating plate range (see section S-1)
2. Check the motor power harness and motor control harness for continuity and good contact. Repair or replace as needed
3. Check the thermostat and wiring to confirm cooling, heating and continuous fan demands
4. Check the blower wheel is seated on the shaft flat, set screw torqued to 165 in-lbs minimum, and wheel has no broken or loose blades
5. Make sure the motor and wheel turn freely with no rubbing on the housing or motor
6. Check the housing for cracks or corrosion and the motor mounting bracket for tight fit and no cracks
7. Only after these pass should you look at the motor itself

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)