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The compressor return port is frosted
The frosting of the compressor air return port indicates that the compressor air return gas temperature is too low, it is known that the refrigerant of the same quality will have different performance if it changes the volume and pressure, that is, if the liquid refrigerant absorbs more heat, then the refrigerant of the same quality will have high pressure, temperature and volume, and if the heat absorption is less, the pressure, temperature and volume will be low.
There are two causes of this problem:
1, the throttle liquid refrigerant supply is normal, but the evaporator can not normally absorb heat to supply refrigerant expansion.
2, the evaporator heat absorption work normally, but the throttle valve refrigerant supply is too much, that is, the refrigerant flow is too much, we usually understand as more fluorine, that is, more fluorine will also cause low pressure.
The compressor return air frosts due to the lack of fluorine
1, because the flow of the refrigerant is particularly small, it will cause the refrigerant to expand from the back end of the throttle valve after the first expandable space began to expand, most of us see the expansion valve at the back end of the liquid head frost is often due to lack of fluorine or the expansion valve flow is not enough caused by too little refrigerant expansion will not use the whole evaporator area, only in the evaporator local formation of low temperature, Due to the small amount of refrigerant in some areas, the rapid expansion of the local temperature is too low, and the evaporator frost phenomenon appears.
After local frosting, due to the formation of a thermal insulation layer on the surface of the evaporator and the low heat transfer in the area, the refrigerant expansion is transferred to other areas, and gradually the whole evaporator frosts or freezes, the whole evaporator forms a thermal insulation layer, so the expansion spreads to the compressor return gas pipe resulting in the compressor return gas frosting.
2. Due to the small amount of refrigerant, the evaporator evaporation pressure is low resulting in low evaporation temperature, which will gradually lead to evaporator condensation forming a heat insulation layer and transfer the expansion point to the compressor return air leading to compressor return air frosting. The above two points will show the evaporator frosting before the compressor return air frosting.
In fact, in most cases for the frost phenomenon, as long as the adjustment of the hot gas bypass valve on the line, the specific method is to open the rear end cover of the hot gas bypass valve, and then use the No. 8 hex wrench, clockwise turn the adjustment nut inside, the adjustment process is not too fast, generally turn about half a circle to pause, let the system run for a period of time to see the frost situation before deciding whether to continue to adjust. When the operation is stable and the frosting phenomenon of the compressor disappears, tighten the end cover.
Cylinder head frost (crankcase frost in severe cases)
Cylinder head frost is caused by a large amount of wet steam or refrigerant drawn into the compressor. The main reasons for this are:
1. The opening of the thermal expansion valve is adjusted too large, and the installation of the temperature sensing bag is wrong or fixed loosely, so that the felt temperature is too high and the valve core is abnormally opened. Thermal expansion valve is a direct acting proportional regulator which uses the superheat at the outlet of the evaporator as a feedback signal and generates a deviation signal after comparing with the given superheat value to adjust the refrigerant flow into the evaporator. It integrates the transmitter, the regulator and the actuator.
Thermal expansion valves can be divided into internal balanced thermal expansion valves and external balanced thermal expansion valves according to different balancing methods. The liquid refrigerant evaporates and absorbs heat in the evaporator, and when it flows to the evaporator outlet, it has been completely vaporized and has a certain superheat. The thermal expansion valve temperature sensing cylinder is close to the evaporator outlet pipe and feels the temperature of the evaporator outlet. If the liquid filled in the temperature envelope is the same as the refrigerant, the liquid pressure above the thermal expansion valve diaphragm is greater than the liquid pressure below the diaphragm, and the higher the temperature at the evaporator outlet, that is, the greater the superheat, the greater the liquid pressure above the diaphragm.
2. When the liquid supply solenoid valve leaks or stops, the expansion valve is not tightly closed, resulting in a large amount of refrigerant liquid accumulated in the evaporator before starting. The temperature relay is used in conjunction with the solenoid valve to control the temperature of the warehouse.
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 setting value, the temperature relay contact is connected, the solenoid valve coil is energized, the valve is opened, and the refrigerant enters the evaporator to cool down. When the reservoir temperature is lower than the lower limit of its setting value, the temperature relay contact is disconnected, the solenoid coil current is cut off, the solenoid valve is closed, and the refrigerant stops entering the evaporator, so that the reservoir temperature can be controlled within the required range.
3. When starting the compressor, the suction stop valve is opened too large or too early.
4. When there is too much refrigerant in the system, the liquid level in the condenser is higher, the condensation heat transfer area is reduced, so that the condensation pressure is increased, that is, the pressure before the expansion valve is increased, the refrigeration dose into the evaporator is increased, the liquid refrigerant cannot be completely evaporated in the evaporator, so the compressor inhales wet steam, the cylinder hair is cold or even frosted, and may cause "liquid blow". At the same time the evaporation pressure will be high.
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