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At present, many units in the market are constructed according to the following ideas: mixing refrigerant with refrigerant, separating refrigerant from refrigerant by oil separator, and then returning refrigerant to compressor through full-liquid evaporator. The refrigeration effect of this type of machine is good and its popularization is great, but there is a problem in its operation, that is, it is easy to "run off the oil", that is, when the cooling water temperature is low, the exhaust superheat is not high, so the separation of oil and refrigerant is not complete, the mixture entering the heat exchanger will lead to the low pressure of the unit, or even the expansion valve. The blockage prevented the unit from starting.

The failure phenomena are as follows:

1. There is no trace of any oil in the oil separator. All the oil comes into the condenser with the exhaust gas. If the water temperature keeps low, all the oil will converge into the condenser and cause oil blockage in the expansion valve. The pressure in the evaporator begins to decrease due to insufficient liquid supply until the low-pressure alarm stops.

2. There is no trace of oil in the oil separator. At the moment, oil does not collect in the condenser, but enters the evaporator through the expansion valve. Oil will stick to the copper tube of heat exchanger of the evaporator, which makes the evaporation effect of the evaporator bad, causes the pressure in the evaporator to be low, and makes the suction superheat of the compressor very low. When the refrigerant liquid is directly inhaled and the exhaust temperature of the compressor is very low, the oil and refrigerant can not be separated. Such a vicious cycle will make all the oil gather in the evaporator. The compressor will stop because of the insufficient oil supply, and even the oil level alarm of the oil separator of the unit.