The frosting direction of the refrigeration system is exquisite, do you know?

1、 Frosting direction if it is the compressor air return port begins to frost towards the evaporator The possible reasons are as follows: 1 The throttle valve is opened too large, which means that the temperature and pressure of condensate return liquid are normal or slightly high, and the frost is gradually formed from the return port of compressor to the direction of evaporator 2 The evaporator can't absorb heat normally, or the cold produced by the evaporator can't be taken away The appearance is that the temperature and pressure of the return liquid are normal or slightly low, and the frost begins from the air return port of the compressor to the evaporator gradually After a long time, all the sections from the air return port of the compressor to the evaporator and from the throttle valve to the evaporator are frozen, and low pressure appears after Zui The inspection methods are as follows: · check whether the air filter screen is clean; · check whether the fan speed is normal; · check whether the evaporator is clean; · check whether the air supply system is blocked; · check whether the belt is too loose 2 If the frosting direction is from expansion valve to evaporator, the possible reasons are as follows: 1 There is little refrigerant (leakage) The appearance is that the return liquid temperature of the condenser is too high but the pressure is not high, and the frost begins from the throttle valve to the evaporator 2 The opening of expansion valve is too small The appearance is that the temperature and pressure of condensate return liquid are normal or slightly low, and frosting starts from the throttle valve to the evaporator 3 Check the sight glass to see the refrigerant condition If the bubbles are serious, it may be system leakage; if the refrigerant in the sight glass does not bubble or rarely bubbles, it may be that the expansion valve is opened too small or blocked, generally there will be a large temperature difference before and after the blockage The surface of the evaporator fins is frosted, and the temperature of the evaporator at the frosted part is lower than 0 ℃ The frosting speed is related to the ambient temperature and humidity There are two phenomena of evaporator frosting: 1) one is frosting from the outlet of the evaporator, and the whole evaporator surface will be covered with frost over time This phenomenon is caused by too much liquid supply to the evaporator (the reaction of capillary system is obvious) For the whole refrigeration system of household air conditioner, it may be caused by the problem of return air system and control system: A due to dust blockage of return air filter screen, dust blockage on the surface of evaporator fins, bad fan capacitance or small capacitance, no rotation of fan motor, slow rotation speed and other reasons, the heat exchange load of evaporator is reduced B long time refrigeration operation when the ambient temperature is low or when the resistance of return air temperature sensor changes In the household air conditioner, if the control system has anti freezing protection function, when the temperature of evaporator coil is lower than 0 ℃ after the refrigeration system runs for a period of time, the controller will automatically shut down the compressor and outdoor fan for protection, and the indoor fan will run with high-speed wind During the protection period, when the temperature of indoor evaporator coil is higher than 10 ℃, the protection will be cancelled to resume the refrigeration work If it is found that the surface of the evaporator is frosted for a long time, it is possible that the evaporator coil sensor and return air temperature sensor of the control system are faulty or the control system has no anti freezing protection function C some air conditioners have continuous operation function When the continuous operation function is turned on, the operation of the refrigeration system is not controlled by the temperature of the temperature sensor If the operation time is long, frost will also appear on the surface of the evaporator Just turn off the continuous operation function During the maintenance, check the evaporator fins, fan system, return air temperature of controller and coil temperature sensor, and the ambient temperature at the time of operation, and confirm that there is no problem in the components before judging whether the system has more fluorine injection The fluorine content rate is usually a phenomenon that may occur after the system is refilled with refrigerants It should be noted that the fluorine content rate of the system may not frost on the surface of the evaporator when it operates at a high ambient temperature, and may frost on the surface of the evaporator when it operates at a low ambient temperature 2) another phenomenon is that the frost starts after the capillary throttling As time goes on, part of the surface at the inlet of the evaporator is frosted seriously, and most of the surface of the evaporator is free of dew This phenomenon is a manifestation of insufficient liquid supply for the evaporator of the refrigeration system For the whole refrigeration system of household air conditioner, it may be that the system has leakage or the throttling system has half blockage There is leakage in the distinguishing system or half blockage in the throttling system: a the air temperature of the condenser is high, the current is large, and some parts of the evaporator inlet are frosted and uncooled, mostly the throttling system has half blockage The filter in front of the inlet of the capillary at the fault position is dirty or the indoor and outdoor connecting liquid pipes (thin pipes) are flattened to form a secondary throttle B the air outlet temperature of the condenser is not high, the current is small, part of the evaporator inlet is frosted and not refrigerated, most of which are the leakage points of the refrigeration system pipeline The system pipeline, welding point, interface carrier, valve core, valve cap, especially the part with oil stain at the system pipeline In the control system of household air conditioner, there should be system capability protection function In the refrigeration working mode, after 30 minutes of continuous operation of the compressor, the temperature of the indoor evaporator coil ≥ 25 ℃ (some factories and households indoor environment temperature - indoor coil temperature ≤ 4 ℃), stop the compressor and the outdoor fan, and the indoor fan operates according to the set wind speed Entering the protection generally requires power failure to exit Some control systems do not have the ability to protect the function In the continuous operation of the compressor, overheating protection of the compressor may occur 3 The evaporator freezes The whole evaporator freezes because the refrigerant in the evaporator is in the process of vaporization and heat absorption! No more calories! Reduce the temperature in the limited space of the outer wall of the copper tube to below 0 ℃! That is, after the temperature of cooling medium (air) is lower than the dew point temperature, dew drops are formed on the outer wall of evaporator! The temperature drops below 0 degrees! Cause ice! Why is the temperature below 0! Because the outer surface of the evaporator is treated with a small amount of air! So heat transfer is better! So the first two analyses of mottled bamboo are all about why the air volume is not enough! As for the third point: if the outlet of evaporator freezes and the superheat of return gas decreases! There may be too much refrigerant! Because one of the necessary conditions for the evaporator to freeze is that the evaporation temperature must be lower than 0 ℃! And more refrigerants will cause the evaporation temperature to rise! Add a little impossible factor: the enthalpy value of the air inlet state point of the evaporator is small! That is, the air inlet temperature is low or the humidity is small! In addition, the evaporator manufacturing process does not use hydrophilic treatment! The condensate can not leave the evaporator smoothly! Too long heat exchange time! 1 Less refrigerant 　 In the case of lack of refrigerant, the pressure in the system will be correspondingly reduced, and the pressure reduction will cause the evaporation temperature of refrigerant to be reduced, usually below zero ℃, which will cause the water in the air to condense directly into frost instead of normal water At the same time, in this case, the unit coil temperature sensing probe in the split air conditioning room (to detect the evaporator coil in the room Temperature) it can also detect that there is a certain temperature drop in the coil (if not, the air conditioner will protect the unit) In this case, the indoor unit of split air conditioner will freeze, and the process should be startup - frost on the high-pressure pipe of the external unit - frost at the inlet of the evaporator of the internal unit - ice on the internal unit - ice on the air outlet (when serious) - internal fan stuck (when serious) 2 The evaporator is dirty When the evaporator of the internal unit is very dirty, the air volume of the internal unit will be seriously reduced, so that the heat absorbed by the refrigerant during the evaporation of the internal unit cannot be replenished from the indoor hot air (I don't understand the change of the evaporation temperature of the refrigerant in this case, and expect someone to replenish it) At this time, the evaporator of the internal unit will also slowly start from condensation to icing And the process should be start-up - the wind is small (the effect of the air outlet is good, but the indoor temperature can't fall down, sometimes there will be mist like water vapor blowing out of the air outlet This phenomenon is usually found in places with poor operation environment, such as bars, karaoke, barber shop (hairdresser) restaurants, etc 3 The fan speed is slow The situation is very similar to the dirty evaporator, but the operating environment is good after actual observation, the evaporator is clean, and the human body feels the wind speed is low 4 The continuous operation time of air conditioner is too long This kind of state is especially common in some enterprises and institutions, but it mostly occurs in the larger cabinet type internal machine The small split hanging machine generally does not appear this kind of situation (it is estimated that it is related to the low cooling capacity) In the larger one, especially in the 5P air conditioner, it will also freeze after a long time of operation, but the part of the ice is different from the above several situations, and the part of the ice is generally frozen It is near the end of the steamer, especially in the air return pipe of the external machine (low pressure, suction) Sometimes the ice will be very thick But this state does not affect its cooling effect 5 The indoor humidity is too high and the operation time is too long It is similar to the previous situation, but it mostly occurs in the split hanging machine, especially in the kitchen room, cold dish room and other places in some hotels, which need a long time to run, and its environment humidity is very high 6 The connecting copper pipes of internal and external machines are bent This kind of situation also happens frequently, and the states that it shows are mostly frosting or icing from the flattened place (icing for longer running time) Explore the reasons It should be that the refrigerant has a secondary throttling at the place where it flows through the flattening, and there should be no evaporation at the place where it is throttled, and most of the flattening places are unable to exchange heat with the outside air, resulting in the temperature at the flattening place getting lower and lower, so Zui ends the ice.