Things You'll Need
SAE 20 nondetergent oil
Lightweight spray lubricant
Keep your fan dry to prevent electrical hazards. Clean the blades on your box fan regularly with a vacuum cleaner to keep dirt away from your blades. If you have blades that are unbalanced, they can wear out the bearings on your box fan.
Never work on a box fan without unplugging it first. Never operate your box fan near a sink or bath tub. Unless it is a window fan, don't leave a fan in an open window while it is raining.
How to Fix a Box Fan. Box fans work by having a set of fan blades attached on the shaft of a small motor. The motors and bearings on box fans have a tendency to go bad. Here is how to fix a box fan.
Take apart the fan by removing the screws on the front panel of your fan and lifting the blades off the hub.
Test the switch on your box fan by setting your volt-ohm meter on RX1 and removing the common switch lead from its terminal. Insert one of the probes into the terminal. Remove the other switch leads and insert the second probe into the terminals. Test each terminal one at a time. All readings should be drawing zero ohms. If they aren't, you will have to either replace the terminals, or if you can't replace them, you will have to replace the fan.
Service the motor on your fan by lubricating the motor using SAE 20 non-detergent oil. Apply one or two drops to each oil port. Test the motor to see if it is working.
Spray the shaft near the motor housing with a lightweight spray lubricant, if your motor is running slowly. Lubrication usually helps.
Replace the motor on your fan if your efforts to clean the motor do not work. You can replace the motor by unscrewing the motor parts, taking the old motor to your local electrical store, purchasing a new motor of the exact same model and installing the new motor.
Put your box fan back together the same way you took it apart.