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Why does the refrigeration compressor frost and the solution!

Why does the refrigeration compressor frost and the solution! 1. The frost on the compressor return air port indicates that the temperature of the compressor return air is too low, so what will cause the compressor return air temperature to be too low? It is known that if the refrigerant of the same quality changes the volume and pressure, the temperature will have different performances. That is, if the liquid refrigerant absorbs more heat, the refrigerant of the same quality will show higher pressure, temperature, and volume. If the heat is less, the pressure, temperature and volume will be lower. Well, if the compressor return air temperature is low, the return air pressure is generally low and the same volume of refrigerant is high. The root cause of this situation is that the refrigerant flowing through the evaporator cannot fully absorb itself and expand to a predetermined pressure. The heat required for the temperature value causes the temperature, pressure and volume values ​​of the return air to be relatively low. There are two causes of this problem: 1. The supply of liquid refrigerant in the throttle valve is normal but the evaporator cannot absorb heat normally and the refrigerant expands. 2. The heat absorption of the evaporator works normally but the refrigerant supply of the throttle valve is too much, that is, the refrigerant flow is too much. We usually understand that there is too much fluorine, which means that too much fluorine will also cause low pressure. Second, due to the lack of fluorine, the compressor returns frost 1. Due to the extremely low flow rate of refrigerant, the refrigerant will start to expand from the first expandable space after flowing out of the rear end of the throttle valve. Due to insufficient flow rate, too little refrigerant expansion will not use the entire evaporator area, only low temperature will be formed in the evaporator, and the local temperature is too low in some areas due to the rapid expansion of the refrigerant, and the evaporator frost phenomenon occurs . After partial frosting, due to the formation of a heat-insulating layer on the surface of the evaporator and the heat transfer in this area is low, the refrigerant expansion will be transferred to other areas, and the frost or ice phenomenon of the entire evaporator gradually appears, and the entire evaporator forms heat insulation Layer, so the expansion will spread to the compressor return pipe and cause the compressor return gas to frost. 2. Due to the low amount of refrigerant, the low evaporation pressure of the evaporator leads to a low evaporation temperature, and it will gradually cause the evaporator to form a heat insulation layer and transfer the expansion point to the compressor return air to cause frost on the compressor return air. Both of the above points will show frost on the evaporator before frost on the compressor return air. In fact, in most cases, the frost phenomenon is as long as the hot gas bypass valve is adjusted. The specific method is to open the rear end cover of the hot gas bypass valve, and then use a No. 8 Allen wrench to turn the adjustment nut clockwise. If it is too fast, it will generally pause for about half a turn, let the system run for a period of time, and then decide whether to continue adjusting after seeing the frost. After the operation is stable, the frost phenomenon of the compressor disappears, and then tighten the end cover. For models below 15 cubic meters, since there is no hot gas bypass valve, if the frost phenomenon is serious, you can properly increase the take-off pressure of the condensing fan pressure switch. The specific method is to first find the pressure switch, remove the pressure switch's adjusting nut to fix the small piece, and then use a Phillips screwdriver to rotate clockwise. The entire adjustment also needs to be carried out slowly. 3. The frost on the cylinder head (crankcase frost in severe cases) is always caused by a large amount of wet steam or refrigerant sucked into the compressor. The main reasons for this situation are: 1. The opening of the thermal expansion valve is adjusted too large, the temperature sensor is installed incorrectly or the fixing is loose, so that the temperature is too high and the valve core is opened abnormally. The thermal expansion valve is a direct-acting proportional regulator that uses the superheat at the outlet of the evaporator as a feedback signal and compares it with a given superheat value to generate a deviation signal to adjust the refrigerant flow into the evaporator. Letter, regulator and actuator in one. When the parameter measured by the sender deviates from the given value, the physical quantity of the sender changes and generates enough energy to directly drive the actuator. The position change of the actuator is proportional to the adjusted parameter. The thermal expansion valve can be divided into two types: internal balance type thermal expansion valve and external balance type thermal expansion valve according to different balance methods. The liquid refrigerant evaporates and absorbs heat in the evaporator. When it flows to the outlet of the evaporator, it has completely vaporized and has a certain degree of superheat. The temperature-sensing cylinder of the thermal expansion valve is close to the outlet pipe of the evaporator, and the temperature of the outlet of the evaporator is felt. If the liquid filled in the warm pack is the same as the refrigerant, the liquid pressure above the diaphragm of the thermal expansion valve is greater than the liquid pressure below the diaphragm, and the higher the temperature of the evaporator outlet, that is, the greater the superheat, the higher the The greater the liquid pressure. This pressure difference is balanced by the tension of the adjusting spring under the diaphragm through the ejector rod. If the tension of the adjusting spring is changed, the jacking force of the jack can be changed, thereby changing the opening of the needle valve. Obviously, the degree of superheat of the evaporator will also cause changes in the opening of the needle valve. When the adjustment spring is adjusted to a certain position, the expansion valve will automatically change the opening of the needle valve according to the temperature of the evaporator outlet to keep the evaporator outlet superheat at a certain value. The opening of the thermal expansion valve is adjusted too large, the temperature sensor is installed incorrectly or the fixing is loose, so that the temperature is too high and the valve core is abnormally opened, causing a large amount of wet steam to be sucked into the compressor and causing frost on the cylinder head. The thermal expansion valve is used in conjunction with the adjustment of the superheat when the evaporator is working. If the superheat of the evaporator outlet is too large, the superheating section at the rear of the evaporator is too long, and the cooling capacity will be significantly reduced. If the superheat of the outlet is too small, it may cause compressor liquid blow or even frost on the cylinder head. It is generally believed that the expansion valve should be adjusted to the working superheat of the evaporator outlet at 3℃～8℃. 2. The liquid supply solenoid valve leaks or the expansion valve is not closed tightly during shutdown, resulting in a large amount of refrigerant liquid already accumulated in the evaporator before starting. The temperature relay is used in conjunction with the solenoid valve to control the warehouse temperature. The temperature sensing package of the temperature relay is placed in the cold storage. When the temperature of the cold storage is higher than the upper limit of the starting set value, the temperature relay contact is closed, the solenoid valve coil is energized, the valve is opened, and the refrigerant enters the evaporator to cool down; when the temperature of the storage is low At the lower limit of its setting value, the temperature relay contact is opened, the solenoid valve coil current is cut off, the solenoid valve is closed, and the refrigerant stops entering the evaporator, so that the storage temperature can be controlled within the required range. 3. The opening of the suction cut-off valve is too large or too early when the compressor is started. 4. When there is too much refrigerant in the system, the liquid level in the condenser is high, and the area of ​​condensation heat exchange is reduced, which increases the condensation pressure, that is, the pressure in front of the expansion valve increases, the amount of refrigerant flowing into the evaporator increases, and liquid refrigeration The agent cannot be completely evaporated in the evaporator, so the compressor sucks in wet steam, the cylinder is cold or even frosted, and may cause "liquid strike", and the evaporation pressure will be high.

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