Gas expansion thermostat in conventional refrigerators

It resembles a light switch that opens and closes an electrical circuit, with the difference that in the refrigerator the thermostat works automatically; it is a device consisting of a capillary tube or bulb attached to the evaporator wall. When the temperature changes, the gas in the bulb increases or decreases in volume causing the diaphragm to expand or contract. As the thermostat terminals are connected in series with the motor, when expanding or contracting, the diaphragm opens and closes the contacts by turning the motor on or off.