Most electric refrigerators are designed with more cooling capacity than needed. Thus, in normal use, they don't work all the time. To get the correct temperature cooling the engine should be turned off when you achieve the desired temperature is low. She turned again, when the evaporator is heated to a certain temperature. Two main types of engine controls are used to enable the motors on and off:
Temperature-driven control engine (thermostatic).
Pressure-wheel motor control (low pressure).
Thermostatic control is the most popular, especially in smaller plants. Thermostatic temperature control, Fig. 4-25, has sensing bulb. Sensitive lamp is connected capillary tube to a diaphragm or bellows. This element is charged with volatile liquids. The fluid expands to increase the pressure of the ball becomes warmer. He again will be contracted to reduce the pressure, because the lamp has cooled.
As the ball, the pressure increases, the diaphragm moves. Since it is connected to a switch or switches actions, he will turn this switch (close loop).
As the lamp cools, a diaphragm or bellows moving in the other direction. Toggle switch will move (to open circuit).
These controls have adjustments that allow for differences in operating temperatures. Many of the controls have a manual switch. This switch allows to disable or enable the system at will. They may also include overload relay. This will open the switch when the device draws too much current.
Thermostats can also be electrically connected timers for automatic defrost the evaporator. Many commercial use units of pressure-driven motor control. She opens a circuit when the pressure drops enough. He closed when the pressure has risen enough. Pressure operated motor control can be used with TEV. It can also be used with high or low side of refrigerant management system.
Steam pressure in the low pressure side changes and temperature. Thus, the pressure can mean temperature. This allows you to use pressure to control the start and stop the engine. Therefore, the relay of pressure, temperature Cabinet.
Air-Conditioning 
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