Collect! The most comprehensive knowledge of refrigeration oil will definitely be useful in the future!

February 20, 2024

        Collect! The most comprehensive knowledge of refrigeration oil will definitely be useful in the future!


1. Classification of refrigeration oil

One type is traditional mineral oil; Another type is synthetic polyol ester oils such as PO, commonly referred to as polyester oil, which is also synthetic polyethylene glycol lubricating oil. Their Chinese names are not very consistent. POE oil can not only be well used in HFC refrigerant systems, but also in hydrocarbon refrigerants. PAG oil can be used in systems with HFC, hydrocarbons, and ammonia as refrigerants.

The main functions of refrigeration oil

Reduce friction work, friction heat, and wear;

Fill the sealing area with oil to ensure sealing performance and prevent refrigerant leakage;

The movement of oil takes away the debris generated by metal friction, playing a role in cleaning the friction surface

Provide hydraulic power for the unloading mechanism.


2. Performance requirements for refrigeration oil

Appropriate viscosity: The viscosity of refrigeration oil should not only ensure good lubrication of the friction surfaces of various moving parts, but also take away some heat from the refrigeration machine and play a sealing role. If the refrigerant used in the refrigeration machine has a high degree of mutual solubility with the refrigeration oil, it is necessary to consider using oil with higher viscosity to overcome the effect of lubricating oil being diluted by the refrigerant.

Low volatility, high flash point: The greater the volatility of the refrigeration oil, the more oil is circulated with the refrigerant. Therefore, it is required that the distillate range of the refrigeration oil be narrower and better, and the flash point should be higher than the exhaust temperature of the refrigeration machine by 25-30 ℃.

Good chemical stability and thermal oxidation stability: The final compression temperature during the operation of the refrigeration machine can reach 130 ℃~160 ℃. At this temperature, the refrigeration oil will be heated and continuously decompose and deteriorate, generating carbon deposits, which can cause the refrigeration machine to malfunction and wear. Moreover, the decomposition products of oil will react chemically with the refrigerant, deteriorating the refrigeration effect, and the acidic substances generated will strongly corrode the refrigeration machine components.

No water and impurities: Because water freezes in the evaporator and affects heating efficiency, contact with refrigerant will accelerate refrigerant decomposition and corrode equipment, so the refrigeration oil must not contain water and impurities.

Other: The refrigeration engine oil should also have good anti foaming properties, and should not dissolve or expand materials such as rubber and enameled wire. Good electrical insulation should be maintained when used in enclosed refrigerators.


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3. Factors to consider when selecting refrigeration oil

Viscosity: The higher the speed of the compressor, the higher the viscosity of the refrigeration oil used.

Thermal stability: Thermal stability is generally measured by the flash point of refrigeration oil. Flash point refers to the temperature at which the vapor of the refrigeration engine oil ignites upon contact with fire. The flash point of the refrigeration oil must be higher than the discharge temperature of the compressor, for example, the flash point of the refrigeration oil used in R717 and R22 compressors should be above 160 ℃.

Liquidity: The refrigeration oil should have good fluidity at low temperatures. In the evaporator, due to low temperature and increased viscosity of the oil, the fluidity deteriorates. When a certain temperature is reached, the refrigeration oil stops flowing, and this temperature is called the freezing point of the oil. The freezing point of the refrigeration oil in a refrigerator is required to be low, especially for low-temperature refrigerators where the freezing point of the oil is crucial.

Solubility: Various refrigerants and refrigeration oil are different in their solubility and can be roughly divided into three categories: one is insoluble in each other, one is infinitely soluble in each other, and the other is intermediate between the two.

Cloud point: The temperature at which paraffin begins to precipitate (oil becomes cloudy) in the refrigeration oil is called the cloud point. When refrigerant is present, the cloud point of the refrigeration oil will decrease.

4. The main reasons for the deterioration of refrigeration oil

Mixing water: Due to the infiltration of air into the refrigeration system, the water in the air comes into contact with the refrigeration oil and mixes in; When there is a high water content in the refrigerant, it can also cause water to mix with the refrigeration oil. After water is mixed in the refrigeration oil, the viscosity decreases, causing corrosion to the metal. In Freon refrigeration systems, it can also cause "ice blockage" phenomenon;



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Oxidation: During the use of refrigeration oil, when the exhaust temperature of the compressor is high, it may cause oxidation and deterioration, especially for refrigeration oil with poor chemical stability, which is more prone to deterioration. After a period of time, residues will form in the refrigeration oil, causing lubrication in bearings and other areas to deteriorate. Mixing organic fillers, mechanical impurities, etc. into refrigeration oil can also accelerate its aging or oxidation;

Mixing of refrigeration oil: When several different grades of refrigeration oil are mixed, it can cause a decrease in the viscosity of the refrigeration oil and even damage the formation of the oil film, causing damage to the shaft; If two types of refrigeration oil contain antioxidant additives with different properties, when mixed together, it is possible to produce chemical changes, form precipitates, and affect the lubrication of the compressor. Therefore, attention should be paid when using them.

There are impurities in the refrigeration oil: it may block the pipelines and components of the refrigeration system, such as expansion valves, filters, etc., affecting the flow and circulation of refrigerant, leading to a decrease in refrigeration efficiency or even failure.

5. How to choose refrigeration oil

Choose lubricating oil according to the compression type: There are three types of compressors for refrigerators: piston type, screw type, and centrifugal type. The lubricating oil of the first two types comes into direct contact with the compressed refrigerant, and the mutual influence between the lubricating oil and the refrigerant should be considered. The lubricating oil used for centrifugal type is only used to lubricate the rotor bearings, and can also be selected according to the load and speed.

Choose lubricating oil based on the type of refrigerant: for lubricating oil in direct contact with the refrigerant, the mutual influence between the two should be considered. Refrigerants like Freon can dissolve in mineral oil, so the viscosity grade of the selected lubricating oil should be one grade higher than those using insoluble refrigerants to prevent the lubricating oil from being diluted and unable to guarantee lubrication. In addition, attention should also be paid to whether a small amount of lubricating oil mixed into the refrigerant will affect the operation of the refrigeration system. The coagulation point of refrigeration oil is a quality indicator for checking whether the lubricating oil mixed with the refrigerant has precipitated wax crystals and caused blockage of the refrigeration system.

Choose lubricating oil based on the evaporation temperature of the refrigerant: Generally speaking, for refrigerators with low refrigerant evaporation temperature, low freezing point refrigeration oil should be selected to prevent the lubricating oil carried by the refrigerant into the refrigeration system from condensing on the throttle valve and evaporator, affecting refrigeration efficiency. The freezing point of the lubricating oil used in a refrigerator using ammonia as a refrigerant should be lower than the evaporation temperature. When using Freon as a refrigerant, the condensation point of lubricating oil can be slightly higher than the evaporation temperature.




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