If a capacitor on an electric motor starts to go bad then the electric motor will sit and hum until it gets enough Voltage built up too start turning.
If your electric motor sits and hums for a few minutes but then finally starts up and runs fine after that then the Start Capacitor on the electric motor is going bad and needs replaced.
If the motor just hums and never starts up but the electric motor is not seized and spins freely then your electric motors start capacitor is bad and needs to be replaced.
The Start Capacitor is there to get the electric motor started since it stores a high Voltage that the motor needs to start.