A device for automatically regulating the temperature inside a refrigeration unit by controlling the operation of the compressor. The manually adjustable control knob attached to its operating mechanism is mounted inside the cabinet, usually with two screws. It consists of a gas-charged capillary tube (called a sensing bulb) connected to the operating mechanism. The sensing bulb is attached to the evaporator. The operating mechanism of the thermostat responds to the pressures exerted from the trapped gas within the sensing bulb. As the temperature of the evaporator coil drops, the volume of gas decreases (due to contraction), and thus the amount of pressure exerted upon the accordion-type bellows within the thermostat operating mechanism is reduced, causing the bellows to contract and open a set of contacts, disrupting the flow of current to the compressor motor. With the rising evaporator temperature, the gas expands and exerts more pressure on the bellows.
As a result, the contacts are forced to close by the expanded bellows, restoring the flow of current to the compressor motor.
On some freezer and refrigerator models, the sensing bulb is not attached to On some freezer and refrigerator models, the sethe evaporator, in which case, the temperature of the refrigerated air is transmitted to the operating mechanism.
