What is a blower motor?

Open the lower door of a furnace and the blower compartment is the bottom section: a squirrel-cage wheel inside a metal housing, with the motor mounted through the center of the wheel. Horizontal attic and crawlspace units put the same assembly at one end instead. It generally slides out whole on two bolts once the wiring harness and capacitor lead are unplugged. If you would rather not open anything, listen instead. The rush of air that starts 30 to 60 seconds after the burners fire is this motor coming up to speed.

Airflow is what makes every other component work, and this motor is the source of all of it. A residential system needs about 400 CFM per ton, so a 3-ton air conditioner wants roughly 1,200 CFM crossing the coil; below that, the coil ices in summer and the furnace overheats in winter. Blower motors fail in recognizable ways. Bearings dry out and the motor squeals or grinds, then overheats and trips its thermal limit, so the system runs 10 minutes and stops. Dust cakes the wheel blades and silently steals a third of the airflow. The run capacitor fails, and the motor hums without turning. On an ECM, the electronics module burns out, which is a $300–600 part by itself.

Blower motors mostly die of neglect elsewhere. A clogged filter forces the motor to work against resistance and run hot, so on-time filter changes every 30 to 90 days are the cheapest life extension available. Beyond that, have the blower wheel pulled and washed every 3 to 5 years, or every 2 in a dusty or pet-heavy house, which adds $150–350 to a tune-up. Older PSC motors with oil ports take a few drops of non-detergent 20-weight oil each year, while modern sealed motors need none. Timing: how often to clean a blower wheel.