The Blower Motor: The Part Your Whole System Depends On

The blower is the fan inside the furnace or air handler that moves air through the ducts. It runs in cooling, in heating, and on fan-only, which makes it the hardest-working motor in the house. When it fails, the outdoor unit may still run and the furnace may still light, but nothing arrives at the registers, and in cooling mode the indoor coil ices over within minutes because there is no air moving across it.

Two kinds of blower motor

PSC motors

The older, simpler design, found in most systems more than about a decade old. A single-speed or multi-tap induction motor with a run capacitor. It is inexpensive and robust, but it draws the same power regardless of what the system needs, and it depends on that capacitor. When a PSC motor gets weak, the capacitor is the first suspect.

ECM motors

Electronically commutated motors are the variable-speed type in newer and higher-efficiency systems. They ramp up and down, use far less electricity at low speed, and can hold a target airflow as the filter loads up. The trade-off is a control module on the motor that is sensitive to heat, voltage spikes and, critically, to being asked to work against high static pressure. An ECM motor in restricted ducts runs at the top of its range constantly, and the module is usually what fails.

Early signs

• Weak airflow at the registers with a clean filter, particularly at the ends of long duct runs.
• A squeal or grinding at start-up, which is a bearing on its way out.
• A humming furnace with no air moving. On a PSC motor that is usually the capacitor; on an ECM it may be the module.
• The blower starts, runs briefly, and stops, or runs at the wrong speed. ECM modules fail intermittently before they fail completely.
• A hot, electrical smell from the air handler.
• The indoor coil freezing repeatedly in summer with refrigerant charge confirmed correct.
• The blower running continuously and never shutting off, which can be a control board or a relay rather than the motor, but presents the same way.

Repair or replace the motor

A PSC motor with a failed capacitor is a quick, inexpensive repair. A PSC motor with failed bearings or windings is replaced as a unit. An ECM motor can sometimes be repaired by replacing only the control module if the motor itself tests good, which is a meaningful saving; where the motor and module are integrated, the assembly is replaced. In either case, the blower wheel comes out and gets cleaned, because a wheel caked with dust is out of balance and moves substantially less air than it should.

On a system that is old enough that the blower is one of several parts wearing out, we will say so. A blower motor replacement on a fifteen-year-old system with a tired compressor is not always the wrong choice, but it should be a choice made knowing the age of the rest.

What we measure on a blower call

Static pressure across the air handler, motor current against the data plate, capacitor value on a PSC motor, supply voltage, and the condition of the wheel and the evaporator coil. If static pressure is high, we tell you why: filter type, return size, duct restriction. Replacing a motor into the same conditions that killed it is a repair we would rather not do twice.

Family-owned in Rockwall, licensed and insured. TX HVAC License TACLB2360E. (469) 338-5533.