Thermal expansion valve is the outlet of the evaporator gas refrigerant overheat control expansion valve opening, it is widely used in non-flooded evaporator. In accordance with the different balance, the thermal expansion valve can be divided into two types of balance and external balance. Thermodynamic expansion valve temperature sensing system can be filled with different substances and methods, the main methods are liquid-filled, inflatable, cross-filling liquid, mixed filling and adsorption filling. What are the thermal expansion valve failure? What is the reason? Symptom 1: thermal expansion valve to provide the lack of refrigerant flow (opening small). Symptom II: Expansion valve to provide the refrigerant flow is too large (large opening). Symptom III: Expansion valve sometimes lack of fluid, sometimes too much fluid (fluctuations). Symptom 1: Thermal expansion valve to provide the lack of refrigerant flow (opening small) Reason 1: Ice blocking. Cause 2: dirty block. Reason 3: temperature package filling medium leakage. Reason 4: Temperature sensor package is installed incorrectly. Cause 5: Temperature package failed to feel the exact temperature. Reason 6: Filling medium migration (with MOP function). Reason 7: spool stuck. Reason 8: The choice of expansion valve capacity is too small, excessive heat adjustment and so on. Reason 1: Ice blocking [Cause]: If there is more water in the refrigerant, it may freeze at the throttle of the thermal expansion valve when the evaporation temperature drops below 0 ° C, resulting in "ice blockage." The possible causes of ice block are: 1) The system is not enough time to vacuum, failed to exhaust the moisture inside the pipe. 2) To the system by adding refrigerant or lubricating oil in excess of water. [Occurrence]: Ice blockage typically occurs at the orifice of the expansion valve because here is the lowest temperature and smallest aperture throughout the system. Observe the color of the liquid mirror test strip, you can determine whether the refrigerant contains too much water. [Approach]: Replace the dry filter, get rid of the water in the system pipe; if necessary, need to vacuum, refilling the refrigerant. This article source cooling Encyclopedia public number Reason 2: dirty block [Cause]: There are impurities in the system. Sources of impurities in the refrigeration system are: copper oxide is not cleaned when the welding film is clean, wear and tear of the compressor to produce metal fines, chemicals produced by the reaction of the refrigerator oil and so on. [Occurrence]: In general, dirty blockage occurs at the dry filter. The impurities in the system are intercepted by the filter, resulting in dirty blockage. It may also occur at the orifice of the expansion valve. After the occurrence of dirty block system evaporation pressure becomes lower, the return air temperature, superheat increased, the system back to the oil difficult. [Approach]: For the clogging generated in the drying filter, you need to replace the drying filter. If dirty in the expansion valve flow block, split expansion valve can remove the flow component, carefully cleaned; the need to replace the expansion valve. Reason 3: The temperature sensor filled media leakage [Causes]: If the temperature inside the filling medium leaks, the diaphragm above the loss of the power to open the expansion valve will cause some or all of the expansion valve is closed, the system is very low pressure is low. Common causes include: 1) Breakage of the thermowell capillary. Capillary rupture so that the temperature inside the filling medium leaked, resulting in the correct signal can not be passed to the thermostatic expansion valve actuator mechanism. Possible locations for rupture include the capillary, the junction between the thermowell and the capillary, and the weld between the capillaries and the body cap. This article from the source of refrigeration encyclopedia 2) temperature package and capillary corrosion. If a large amount of highly corrosive material is present in the application environment, they both destroy the passivation layer on the stainless steel surface and thus accelerate the corrosion of the metal. At the same time, there are a large number of solid particles in the atmosphere, and they may also cause pitting corrosion on the metal surface under the solid particles when combined with sulfur dioxide and water. In addition, the rate of corrosion is also related to relative humidity and temperature. 3) temperature package capillary damage. Sharp objects on the capillary scraping, cutting, squeezing or burns, so that the temperature package within the filling medium missing, or plug the capillary, affecting the superheat signal transmitted to the diaphragm cavity, resulting in expansion valve can not be normal jobs. [Approach] This happens, you need to change the expansion valve. Therefore, special requirements in the process of installation and use, to avoid capillary contact with sharp objects, to avoid damage to the burns, the use of protective materials for capillary protection. For pitting corrosion, protective layer and corrosion inhibitor can be used to control the concentration of corrosive gases and solid particles in the atmosphere. Reason 4: Temperature sensor package is installed incorrectly. It is recommended to install the temperature package on the return air pipe near the evaporator outlet. Installation, the temperature package needs to be fixed with the installation of the return pipe surface to rust, if it is steel, rust painted silver paint on the surface, in order to ensure that the temperature sensor and the back of the trachea good contact. This article source cooling encyclopedia public number reason 5: temperature package failed to feel the exact temperature. Temperature at the temperature of the package affected by other factors. Sensing temperature hysteresis, dirt causes heat transfer difficulties. Reason 6: Filling Media Migration (with MOP Function) For MOP-enabled expansion valves, the temperature sensing pack and the valve head are filled with relatively little charge. If the temperature of the valve head is lower than the temperature of the temperature sensing package, the charging medium will also migrate from the temperature sensing package to the valve head, resulting in the expansion valve not working properly. The process of filling medium migration and temperature and time-related. [Approach]: in the transport, storage, installation, commissioning and use of the process to always keep the temperature of the temperature package below the temperature sensing element temperature. If a media misfed condition has occurred, the media can be returned to the temperature sensing package by cooling the thermostat (recommended) or by heating the valve head. The process is affected by temperature and time. Reason 7: Valve core stuck [Cause]: System refrigerant more water, or refrigerant containing corrosive substances, making the expansion valve inside a serious corrosion, resulting in the valve core can not move, the expansion valve can not be adjusted . [Approach]: replace the expansion valve and filter dry, remove the system of water and other impurities. Reason 8: The choice of expansion valve capacity is too small, excessive heat adjustment and so on. Symptom 2: Expansion valve to provide the refrigerant flow is too large (large opening) [Symptoms]: a liquid back phenomenon; low superheat; suction temperature and pressure fluctuations. [Causes]: 1) thermal expansion valve spool stuck. 2) External balance tube plugged. The sensed pressure can not be quickly transmitted to the diaphragm below, resulting in a small valve closing, valve opening larger. This article source cooling encyclopedia 3) temperature package installation problems. Installation location and the wrong way, or poor contact, poor insulation, are likely to cause excessive fluid supply. 4) The selection of the expansion valve cold too much. 5) Thermal expansion valve overheating improperly adjusted. Symptom III: Expansion valve from time to time supply of liquid, sometimes too much liquid (fluctuation) [Causes]: 1) The selection of excessive expansion valve caused by fluctuations in cooling capacity. 2) temperature package installation location is not appropriate. 3) liquid separation head uneven.