A central AC system has two fans: one in the indoor air-handling unit that circulates conditioned air throughout your home, and another in the outdoor condenser unit that prevents overheating in the coils and compressor.
Without functional fans, the evaporator coils' coolant can freeze, which ultimately affects your unit's cooling efficiency. Your AC is virtually useless when the fan motor malfunctions. Below are signs to look out for to identify a faulty blower motor.
The Fan Runs After Switching off the AC
Typically, the fan runs for several minutes after turning off your AC, but it shouldn't run for too long. If the fan keeps running after you switch off your AC, you might have a bad blower motor resistor. The blower motor resistor can fail if it corrodes or overheats.
Consequently, the blower motor maintains one fan speed even when you switch off your system. You might need to replace the resistor to restore the fan's functionality.
A broken relay switch may also cause your fan to run constantly. Relays manage power flow in your air conditioning unit. When these components get stuck or a wiring issue occurs, the fan can't actuate the on and off commands, so it keeps running.
Rattling or Buzzing Noises
If your AC produces loud rattling noises every time the fan is on, debris or loose stones trapped in the condensing unit might be the cause. Also, unbalanced or loose blades striking the fan housing unit cause a rattling noise. You will probably hear a whirring noise if the fan gets loose and begins to fall apart.
For air handling units with belt-driven fans, you might notice loud squealing noises when the fan motor kicks in, which indicates a belt issue. This could also be an indication of failing parts in your fan motor. That's usually a sign that the fan has served its time, and you should replace it.
Fan Blades Turn Slowly
When the fan blades turn slowly, either the motor has come to the end of its life, or something is obstructing the blade's movement. The condenser unit might contain dirt and other buildups that impede a smooth rotation.
Slow-moving blades lower your AC's cooling efficiency due to the weak airflow. When the blades can't move completely, nudge them with a screwdriver to see if they move freely. If they don't, you should have them checked by a repair professional.
Also, check if the fan settings are set at low speed and adjust accordingly. Don't forget to oil the motor bearings for the fan motor to run properly.
A fan motor is the heart of your AC, and you should maintain it properly to keep your system running. If your unit's performance reduces due to these motor issues, reach out to an AC technician for repairs.
Contact an AC repair technician for more information.