Without a fan, your central air conditioner is unable to function at all. The unit may still pop on, but there will be no cool air flowing from the vents. Fortunately, there are only a few issues that commonly affect the fan so you may be able to troubleshoot the problem on your own.
Most older and some newer AC units are belt-driven, which means that there is a belt instead of gears that runs the fan from the motor. Over time, this belt can stretch and loosen, or fail entirely — both issues that result in a non-functioning fan. You may get a warning that the belt is failing. For example, the AC may start making a whining or squealing sound when it is running, or you may even smell burnt rubber as the belt wears through. Fortunately, this is an easy fix since all that is needed is a new belt.
A more alarming issue is if the actual fan motor is failing. Motors often get noisy as they begin to fail, so you will likely have some warning. Grinding noises are relatively common, as are high pitched whines and vibrational noises. Once the motor fails, the lack of noise will alert you to the cause since you won't hear what should be the gentle hum of the motor running and the fan blades rotating. Typically, a failed motor will require replacement, although in some cases the motor may be able to be repaired.
Malfunctioning Contactor Switch
The contactor switch is an electrical component that controls fan and motor operation. The motor won't be turned on if the contactor switch is blown, so you may turn on the AC but nothing will happen. Contactor switches may fail abruptly with no warning, or you may have issues with the switch sometimes functioning and other times failing. The good news is that the switch is easy and cost-effective to replace.
Another electrical component that can lead to fan failure is the capacitor. Capacitors provide the energy to the fan motor, so without them, the fan and motor will not operate and your home will not cool. Much like the contactor switch, a failed capacitor can be quickly replaced so that your AC fan can resume working as normal.
Most AC fan issues can be repaired at a cost much lower than replacement of the entire unit. Contact an AC service in your area for more help.