A control apparatus includes a controller that controls a motor, a first transmission channel connected to a first power-supply terminal of an alternating-current source that supplies an alternating-current voltage, a second transmission channel connected to a second power-supply terminal of the alternating-current source, and a third transmission channel connected to each of the first transmission channel and the second transmission channel. The controller switches the rotational speed of the motor based on the voltage value of a signal input to the controller in accordance with a first connection status of the first transmission channel and the third transmission channel and a second connection status of the second transmission channel and the third transmission channel.