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1. Liquid return: For refrigeration systems using expansion valves, liquid return is closely related to the selection and use of expansion valves. Expansion valve selection is too large, the superheat setting is too small, the installation method of the temperature sensor is incorrect, the insulation bandage is damaged, and the expansion valve failure may cause liquid return.
For small refrigeration systems that use capillaries, excessive liquid addition can cause liquid return. If the evaporator is seriously frosted or the fan fails, the heat transfer becomes worse, and the unevaporated liquid will cause liquid return. Frequent fluctuations in temperature will also cause the expansion valve to fail to respond and cause liquid return.
2. Start with liquid: The phenomenon that the lubricating oil in the compressor violently foams is called start with liquid. The blistering phenomenon when starting with liquid can be clearly observed on the oil sight glass. The fundamental reason is that a large amount of refrigerant dissolved in the lubricant and sinking under the lubricant suddenly boils when the pressure drops suddenly, and causes the foaming phenomenon of the lubricant, which easily causes liquid shock.
3. Exhaust gas temperature is too high: There are several reasons for the high exhaust gas temperature: high return air temperature, large motor heating capacity, high compression ratio, high condensing pressure, adiabatic index of refrigerant, and inappropriate selection of refrigerant.
4.Liquid shock: In order to ensure the safe operation of the compressor and prevent the occurrence of liquid shock, the suction temperature is required to be a little higher than the evaporation temperature, that is, it should have a certain degree of superheat. Under normal circumstances, the suction temperature should be 5～10℃ higher than the evaporation temperature.
5.5. High suction temperature: insufficient refrigerant charge in the system, or too small opening of the expansion valve, clogging of the expansion valve opening, poor heat insulation of the return air pipeline or too long pipeline, etc.
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6. The exhaust temperature is too low: the ice or dirty plug of the throttle valve or the dry filter, and the filter is blocked, and the refrigerant charge is insufficient.
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