Blower motor operating in power, temperature or speed limit (reduced airflow)

What is going on

Furnace is limping along at reduced output. The blower motor has backed itself off on power, temperature or speed because airflow isn't what it expects. Check the filter first. Always the filter first.

Likely causes

• Blocked filters
• Restrictive or undersized ductwork
• High ambient temperatures at the furnace location

Check in this order

1. Check filters for blockage. Clean or replace them, or remove the obstruction.
2. Check ductwork for blockage. Make sure every register is fully open.
3. Verify the ductwork is sized correctly for the system. Resize or replace if needed.
4. Check the installation location requirements for ambient temperature limits.
5. Take a temperature rise reading across the furnace after fixes and compare to the rating plate.
6. Run a full cycle and confirm the blower no longer limits.

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)