In addition to the main winding, the secondary winding is needed to generate rotating magnetic field. There are two kinds of capacitors on the secondary winding, starting capacitor and running capacitor. The starting capacitor is connected in parallel to the secondary winding. It is only turned on when the compressor is started, and the capacitor is disconnected when the compressor is started. Because the torque of the single-phase compressor is small, it is not easy to start, so you need to add the starting capacitor, the starting capacitor is generally speaking, the single-phase compressor needs an external force to make it easy to start. Capacitive induction motor has two windings, namely the starting winding and the running winding. The two windings are 90 degrees apart in space. A capacitor with large capacity is connected to the starting winding. When the running winding and the starting winding pass single-phase AC, the current in the starting winding is 90 degrees ahead of the current in the running winding and reaches the maximum value first due to the effect of the capacitor. Two identical pulsed magnetic fields are formed in time and space, so that a rotating magnetic field is generated in the air gap between the stator and the rotor. Under the action of the rotating magnetic field, the induction current is generated in the motor rotor, and the interaction between the current and the rotating magnetic field generates the electromagnetic field torque, so that the motor rotates. The running capacitor is connected in series to the secondary winding, and its main function is to cooperate with the main winding to generate rotating magnetic field.