Central air conditioner not blowing air?

Depending on the make and model of the air conditioner. It is probably your blower motor. There are two, possibly three items to consider. The motor, the start capacitor and the run capacitor. Some systems will have just the motor and the start capacitor. Some have just the motor and the run capacitor. Usually (not always) the capacitor will show physical signs of failure. Burned terminals, swelling or white stuff coming out of the top. Expect to pay $30 for the capacitors and several hundred for a new blower motor.