Refrigerator is a  reversed heat engine .The reversed heat engine works on the principle of reversed Carnot cycle.

The reversed heat engine transfers the heat from sink to the source with the help of external work.

Reversed carnot cycle-

Carnot cycle is a reversible cycle, and it becomes the Carnot refrigeration cycle when the process reversed. The direction of heat and work interactions are totally reversed, thus Thus,

Heat absorbed from low-temperature-reservoir is Q_l

Heat rejected to a high-temperature-reservoir is Q_h

Work done is W_net-in

Reversed Carnot cycle is same as that of conventional Carnot Cycle except the direction of the processes.

Carnot engine - 

Carnot engine is an ideal heat engine that converts heat energy into mechanical energy.

Carnot cycle made up of four stages-

1. Isothermal expansion

2. Adiabatic expansion

3. Isothermal compression

4. Adiabatic compression