Section 01 Alternatives to HCFCs in the Refrigeration and Air Conditioning Sector 34 Wh en evaluating alternative refrigerants for different applications, careful consideration should be paid to the oil properties and how they are affected by the different refrigerants. How a refrigerant behaves in a system is significantly easier to predict than how the mixture of oil and refrigerant will behave. It is easy to define the properties of a refrigerant or pure oil at different pressures and temperatures. It much more complex to predict and test lubrication properties in the compressor and oil transport in the system after the refrigerant and oil has mixed. The selection of oil must take into account all aspects to ensure long term reliability of the system. Many systems have failed because end users have not considered the interaction between the oil and the refrigerant. 1.5 Oils in refrigeration and air conditioning systems Su mmary Oils in RAC systems W ith a few exceptions, RAC systems contain an oil to seal and lubricate the compressor. A small amount of oil will always leave the compressor and will be transported around the system (even with oil separators, a small amount will circulate in the system). In most systems, oil return requires that the oil is miscible with the refrigerant. The miscibility also decreases the negative impact of oil in the heat exchangers. The oils used with CFCs and HCFCs are not miscible with HFCs, which makes an oil change required to achieve the same characteristics. The Mineral oil (MO), alkylbenzene (AB) and sometimes Poly-alfa-olefins (PAO) oils used with CFC or HCFC refrigerants are most commonly replaced with Polyolester (POE) oils when HFCs are used. Also Polyalkylene glycols (PAG) oils and Polyvinylethers (PVE) are used for HFCs. PAG is the oil used in automotive air conditioning. “Service” or “drop-in” blends are designed to achieve a behaviour similar to that of HFC/MO or HCFC/MO to avoid the cost of changing the oil to a miscible oil. It should be noted that there will be significant differences that will affect some systems considerably. T he new oils for HFCs are hygroscopic and require training and proper handling to avoid increased failure rates. Large cans of oil that cannot be emptied at one installation should not be used unless oil is moved to a pressure vessel, i.e. a two port refrigerant cylinder where it can be kept under overpressure with nitrogen.