1. Viscosity: Viscosity is a major performance index of refrigeration oil. Different refrigerants have different requirements for viscosity. For example, R12 and refrigeration oil can dissolve each other, which will reduce the viscosity of refrigeration oil. Therefore, refrigeration oil with higher viscosity should be selected. It is not good for the viscosity of the refrigerant oil in the compressor to be too high or too small. If the viscosity is too large, the friction power and friction calorific value of the compressor will increase, the starting torque will increase, and the efficiency of the machine will decrease; if the viscosity is too small, the wear of the bearing will be accelerated due to the inability to establish the required oil film. Therefore, the viscosity must be moderate. The viscosity of frozen oil varies greatly with temperature (for example, when the temperature increases from 50 ℃ to 100 ℃, the viscosity of mineral oil decreases to 1/3-1/6 of the original value). Therefore, refrigerant oil with little effect of temperature on viscosity should be selected.

2. cloud point: frozen oil cloud point is that when the temperature is reduced to a certain value, frozen oil began to precipitate paraffin (ie frozen oil becomes turbid) when the temperature. The cloud point of the refrigerant oil used in the refrigeration compressor should be lower than the evaporation temperature of the refrigerant. Especially in the fluorine system, a part of the refrigeration oil is dissolved in the refrigerant and flows with the refrigerant to all parts of the refrigeration system. If paraffin is precipitated in the oil, it will accumulate at the throttle valve to cause blockage, or accumulate on the evaporator The heat transfer surface weakens the heat transfer effect.

3. Freezing point Freezing oil is cooled to the temperature at which it stops flowing under the test conditions, which is called the freezing point. The freezing point of the refrigerating oil used in the refrigeration compressor should be as low as possible. General freezing point should be below -40 ℃. When the refrigerant oil and refrigerant dissolve with each other, the freezing point will be lowered.

4. flash point: frozen oil (in the open oil container) heated to its steam contact with the flame, the lowest temperature flash fire is called the flash point. The flash point of the refrigeration oil used in the refrigeration compressor should be 25-35 ℃ higher than the exhaust temperature, so as not to cause the combustion and coking of the refrigeration oil. Generally, the flash point of refrigeration oil used for ammonia, R12 and R22 should be above 160-170 ℃.

5. The stability and oxidation resistance of frozen oil should have good chemical stability and oxidation resistance, otherwise under the catalytic action of high temperature or metal, contact reaction with refrigerant, etc., will generate coke, acid and other harmful substances.

6. Water content and mechanical impurities: frozen oil should not contain water, because water will not only reduce the evaporation pressure, evaporation temperature, but also aggravate the chemical changes of the oil and the role of corrosive metals. Moisture in the Freon compressor will also cause "steel plating phenomenon", so that copper parts and Freon effect and decomposition of copper, and accumulated in the bearing, valve and other parts of the steel surface. As a result, the thickness of these watches increases, the clearance of the bearings is destroyed, and the machine runs poorly. This phenomenon occurs more often in hermetic and semi-hermetic compressors. Generally, the new oil does not contain moisture and mechanical impurities, because the refrigeration oil used in the refrigerator has undergone strict dehydration treatment in the production process. But the dehydration of frozen oil has a strong hygroscopicity, so in the storage, refueling, should try to avoid contact with the air. Dissolving and diluting the frozen oil with gasoline or benzene, and filtering with filter paper, the residual substance is called the mechanical impurity of the frozen oil. The mechanical impurities in the refrigeration oil will accelerate the wear of parts and the reduction of oil insulation performance, and block the refrigeration oil channel, so the fewer impurities, the better, and the general requirement is not more than 0.01%.

7. Breakdown voltage: Breakdown voltage is an indicator of the insulation performance of refrigeration oil. Pure refrigeration oil has good insulation performance, but when it contains moisture, fiber, dust and other impurities, the insulation performance will be reduced. Semi-hermetic and fully hermetic compressors generally require the breakdown voltage of the freezing oil to be above 25kV. Because the refrigeration oil is in direct contact with the motor windings.