Polyolester

Polyolester oil (POE oil) is a type of synthetic oil used in refrigeration compressors that is compatible with the refrigerants R-134a, R-410A and R-12. It is recommended by experts as a replacement for hydrofluorocarbons (HFCs). Along with R-134a, POE oil is recommended as a replacement for R12 mineral oil as R134a does not mix well with mineral oil. These wax-free oils are suggested for use with chlorine free HFC systems as they provide better lubrication and stability and are more miscible with HFC refrigerants. They can meet the lubricity requirements to those of mineral oils used with CFCs and HFCs. They are compatible with most lubricants in the market. It is noted that the viscosity of the oil decreases with temperature. The dispersion behavior of this oil has also been the subject of a lot of study. It is also considered by some to be a good additive to engine oil.
Use.
The use of this type of oil is in the process of being phased-in by manufacturers who use compressors in their products. The need to replace the old oils has arisen due to environmental restrictions causing incompatibility of the old oils with the new refrigerants. POE oils are very good solvents and easily dissolve most of the residual mineral oils that they may be replacing. So even though small amounts of the old oil may remain, it won't clog the system. 
Polyolester oil is used exclusively in jet turbine engines and often used in moving picture film cameras.
Problems.
However, the same properties that make it a good solvent for oils also make it a good solvent of undesired things left behind during the manufacturing of a unit. Some of which are: dust, dirt, residue from soldering, small bits of metal from cutting, and oxidized metal from the tubing. The residues collected can clog the system filters and cause excessive wear or damage to critical components such as the vanes or valves. This aspect makes it more important to check that components are machined properly, deburred, and cleaned. Another problem with these oils is that they are hygroscopic in nature, which means they can absorb moisture from the atmosphere. Hence, technicians working with units that have to be opened, should leave the unit open for as little time as required.
In addition, POE oils typically have lower viscosity indexes than PAG or PAO oils, so that a higher viscosity grade is required in order to attain a certain kinematic viscosity at higher oil temperatures.