There are numerous reasons why a blower motor may fail. The first one that comes to mind is quite obvious and that would be age. Lets face it, not too many things get better with age, and blower motors would be one of them that don’t. As motors age, they are subject to constant abuse from moisture and heat. This causes the interior components to wear and eventually the motor will give out.
Clogged air filter
One of the most common reasons for premature failure would be running the blower with a clogged air filter. When you run a blower with a clogged air filter, it creates extra stress on the motor. This is because the motor has to work harder to pull the air through that clogged filter. This can cause the motor to overheat. When a motor overheats, it can cause the motor to leak the oil from the bearings and become noisy or lock up. You may have even noticed an oil stain under your blower motor from this.
Failed motor windings
Another issue created by over-heating is wearing on the motor windings. Windings are simply put, a bunch of wire wound around a core. This wire is covered in a layer of clear insulation. As the motor ages, this insulation becomes thinner and thinner until one day it disappears and you get a short. You know if this happens to you because the motor will give off a “humming” sound. Sometimes you may be able to spin the motor by hand and pass this spot on the winding and get the motor to start.
Blocked motor cooling plate
Overheating is common on motors when the cooling plate is clogged up from lack of maintenance and clogged air filters. (Photo shown above of motor with clogged cooling plate)
Clogged/Dirty blower wheel
Yet another maintenance caused motor premature failure would be from a dirty blower wheel. a dirty blower wheel can cause vibrating noises as well as a lack of airflow. This can ultimately lead to failure because the motor has to work harder to move the air. Each blade on the wheel has a curve to it to “scoop” the air, and when this is covered in a layer of debris, it “flattens” the curve. (shown in the photo above)
Weak start capacitors are another reason why a blower motor could fail. When a capacitor is weak, it causes the motor windings to overheat and prematurely wear. The capacitor could also be so weak that it could cause the motor not to start at all. In this case, you could just replace the capacitor and the motor should start right up and operate normally. However, when a capacitor goes weak to the point of failure, the damage has already been done to the motor and likely won’t last too much longer.
The last reason why a blower motor might fail is a power surge or an electrical short. A power surge happens when a surge of electricity is run through your homes’ wiring and overloads all the sensitive electrical components. An electrical short happens when an uninsulated part of a power supply wire makes contact with the ground.
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