A nonworking box fan can be extremely annoying when room air becomes stale and stifling. Box fans are designed to move air so there's circulation in areas that otherwise would have dead air.
To circulate air more efficiently, most box fans are equipped with a three-speed motor that provides three different speed settings, allowing the user to customize the blast of air to the size of the room.
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The process of repairing a three-speed box fan with a broken switch can be easily accomplished with a new three-speed switch (obtainable from most hardware or home improvement stores; look for a switch with four wires), the manufacturer's wiring diagram (search online for the make and model of fan plus the words "wiring diagram"), wire cutters, wire strippers and wire nuts.
Identify All Fan Wires
Make sure the fan isn't plugged into a power supply. Take the back off the fan to make the motor, switch and wires more readily accessible. Using the fan manufacturer's wiring diagrams as a guide, locate the wires for the three-speed switch and the fan's motor.
The switch will have a single main input wire known as "the line" and three additional wires that control speed. The motor will also have three speed wires and one neutral wire. Wire color coding may vary from manufacturer to manufacturer.
Remove the Old Switch
Take note of the position of the old switch, and mark on the new switch where the wall cord wires connect and where the motor wires connect. Cut the old switch free, snipping the wires as close to the switch as possible. Set the old switch aside.
Connect the Wall Plug
Using the wire stripper, remove a half inch of insulation from the end of each wire, including the two wires from the cord that enters the fan and has a wall plug on the exterior end.
One of the wires in the wall plug cord is a neutral wire, which will connect to the neutral wire from the motor. Twist the stripped ends of these wires together and secure them with a new wire nut.
The other wire from the wall plug cord is the input wire, which will connect to the input wire in the switch. Twist the stripped ends of these wires together and secure them with a new wire nut.
Connect the Switch to the Motor
Using the manufacturer's wiring diagram, locate the low-speed wire from the fan motor and the low-speed wire from the switch. Twist the stripped ends of these wires together and secure them with a new wire nut. Continue by connecting the medium-speed wires from the motor and switch and the high-speed wires from the motor and switch in the same fashion.
Route the Wires Away From the Fan Blades
Ensure no bare wire is exposed or sticking out from the wire nuts. Route the wires so they can be attached to the frame of the box fan using plastic ties and remain safely out of the path of the fan's blades. Reassemble the box fan, make sure the control is set to "Off" and plug the fan in. Test the fan to ensure all three speeds work correctly.
Once the switch is replaced, your box fan should operate correctly again. If the fan still fails to turn on or hums but the blades don't turn, you may have another issue that needs to be addressed.
This method can aid in the replacement of three-speed switches for ceiling fans and fan controllers built into the wall, as well.