The fan motor turns the blades of your ceiling fan, enabling it to cool or circulate air in a room. But the motor can wear out due to age or be defective.
Fortunately, you can test a fan motor to determine what might be wrong. To do so, you'll need a multimeter with an ohms setting.
Electrical Problems
The motor is one of the hardest working components in your air conditioner. It’s important to keep it properly maintained to avoid electrical and mechanical problems that can lead to failure.
Electrical problems with a fan motor can include wires that get frayed or disconnected, voltage issues or shorted motor windings. It is important that a trained HVAC professional checks for these issues before attempting to make repairs. Working with electrical wiring and motors is dangerous and should be left to the professionals.
If your fan motor has a lot of noise, you may need to check its wiring. Try using a multimeter to see if there is power being supplied to the motor. If not, then the problem is most likely a fuse or relay.
Mechanical Wear and Tear
The term “wear and tear” means the gradual deterioration or damage of a physical asset over time. It is a necessary part of owning and using a machine, but it can be minimized with regular maintenance and checks.
Mechanical wear occurs in individual machine parts due to abrasion or corrosion. For example, the insulating material between motor shaft bearings can erode, which increases operating temperatures and leads to failure. Corrosive wear can also result from impact on the bearings’ outer raceways or balls, causing pitting and reducing their ability to support a load.
To check for mechanical wear, you can test the motor with a multimeter. Make sure that the meter is set to the ohm setting and touch the probes of the meter to the motor terminals. An infinite reading indicates that the motor is faulty. By understanding what is considered normal wear and tear, you can make an accurate distinction between property damage and natural rental depreciation when inspecting a tenant’s apartment and when writing up the move-in and move-out checklists.
Overheating
Many industrial fan motors are rated to operate in specific ambient temperatures. If your motor is operated in a much warmer environment than the temperature it was designed for, it will struggle to disperse heat and could overheat.
A rattling noise or smell from the fan motor may indicate that it is overheating. If you can, try to remove the screws that hold the fan in place and take it out carefully, without damaging any wires. Then, you can clean the bushings and bearings – though you should only do this if you know what you’re doing.
Other causes of overheating include a bad start run capacitor or incorrectly sized fan blade, which leads to overamping. Dirt buildup also can cause the motor to overheat as it struggles to vent itself properly. Fuses and circuit breakers are often used to protect against electrical overloads. However, if these protective devices fail or are bypassed, overheating is more likely to occur.
Damaged Bearings
The bearings in an electric motor have a sliding or clearance fit with the end shield and shaft. This is to allow the bearings to expand and contract with temperature changes while keeping them in place. A large difference in shaft and housing temperatures can cause the bearing inner race to spin on the shaft journal creating metal-to-metal friction and destroying the shaft surface, leaving micro craters that resemble grey striations. This is known as fluting and results in shortened bearing life.
Electrical discharges in the presence of a magnetic field can also damage bearings by rapidly discharging current in the lubricant film. The resulting high-frequency current pulses cause localized voltage in the bearing.
To prevent this type of damage, modern shaft grounding rings are used to provide a low impedance path from the motor frame to the motor's shaft using conductive microfibers. This method is far more reliable than the older single-point contact brushes and eliminates the problems of clogging, overheating and erratic current flow.