The working principle of refrigerator thermostat

The temperature controller uses the principle of pressure to push the contacts on and off. Its structure is composed of a bellows, temperature bulb (test tube), eccentric wheel, micro switch, etc. to form a sealed induction system and a signal power transmission system. There are generally two control methods; one is controlled by the temperature change of the object to be cooled, mostly using a vapor pressure type temperature controller, and the other is controlled by the temperature difference of the object being cooled, mostly using electronic temperature Controller. The thermostat is divided into: Mechanical type is divided into: steam pressure type thermostat, liquid expansion type thermostat, gas adsorption type thermostat, metal expansion type thermostat. Among them, the vapor pressure type thermostat is divided into: inflatable type, liquid-gas mixed type and liquid filled type. The mechanical type of household air conditioner is mainly based on this kind of thermostat. Electronic type is divided into: resistance type thermostat and thermocouple type thermostat. The main components of the circuit system are: temperature controller, thermal protector, main control switch, running capacitor, fan motor running capacitor. The function of the temperature controller is only to control the start and stop of the compressor. Working principle Vapor pressure type The action of the bellows acts on the spring. The elastic force of the spring is controlled by the knob on the control panel. The capillary tube is placed in the refrigerator compartment and reacts to the temperature of the indoor circulating return air. When the temperature rises to the set temperature, the temperature-sensing agent gas in the capillary tube and the bellows expands, so that the bellows expands and overcomes the elastic force of the spring to connect the switch contact. At this time, the compressor runs and the system cools down again. When the temperature drops to the set temperature, the gas in the temperature sensing bulb shrinks, and the bellows shrinks and acts together with the spring, placing the switch in the off position to cut off the motor circuit of the compressor. Repeated actions to achieve the purpose of temperature control. Electronic temperature controller The electronic temperature controller (resistance type) is measured by the method of resistance temperature sensing. Generally, platinum wire, copper wire, tungsten wire and semiconductor (thermistor, etc.) are used as temperature measuring resistors. These resistances Each has its own advantages. The sensors of household air conditioners are mostly thermistor type. The thermistor thermostat is made according to the principle of Wheatstone bridge, Wheatstone bridge. Connect power E at both ends of BD. According to Kirchhoff's law, when the resistance of the bridge is R1×R4=R2×R3, the potentials of A and C are equal, and no current flows between the output terminals A and C. , The size of the thermistor's resistance R1 changes with the rise or fall of the surrounding temperature, so that the balance is destroyed, and there is an output current between AC. Therefore, when constructing a thermostat, it is easy to change the temperature adjustment range and working temperature by selecting an appropriate thermistor.