Refrigeration systems that contain polyolester (POE) oil present technicians with concerns that aren’t normally found with systems that use mineral-based or alkylbenzene oils. Refrigeration technicians need to be aware of these issues while servicing and installing POE systems, to prevent system problems from developing.

One major concern with POE oils is that they are hygroscopic. If they remain in contact with air, they have the ability to absorb its moisture. For a technician, this means that when a repair requires opening a system, it should only be left exposed to the atmosphere for as long as necessary to complete the repair.

This requires some forethought and planning. When replacing a compressor, for instance, you wouldn’t want to remove its stub cap until you are ready to braze it into the piping. Also, if the system is left open for an extended period (such as overnight), cap it off to prevent the oil from absorbing moisture.


It is normally better to use several smaller containers of POE oil for a particular job rather than one large container for several jobs and have to store the oil between jobs. If unused oil does need to be stored, it should to be stored in its original metal container rather than a plastic container.

POE oil can absorb moisture through the walls of traditional plastic containers. That’s why manufacturers ship new POE oil in metal containers.

Another concern for technicians is the ability of POE oils to be effective detergents. These oils can effectively clean the inner surface of a system, releasing debris that might be present. When converting an existing mineral oil system to use POE oil, it is a good practice to install a suction line filter-drier into the system. This will help filter out the debris released by the POE oil which may clog metering devices or lead to a premature compressor failure.

While brazing copper tubing, it has always been recommended that the tubing be purged with nitrogen to prevent the formation of oxide scale inside. This is even more important when installing and servicing systems containing POE oil. If brazed without the use of nitrogen, the oxide scale formed on the inner tubing can be scrubbed from the walls by the oil and travel throughout the system.

Another concern is the difficulty of removing moisture from POE oils. Moisture will stay dissolved in the oil and cannot be readily removed by applying a vacuum; moisture can only be removed from POE oil with the use of a desiccant. Again, normal servicing practices always recommend replacing the liquid line filter-drier when a system is opened for service. It is even more important with systems using POEs.

Servicing systems with POE oils has some added concerns for service technicians, but following good industry practices will prevent these oils from creating future issues for the system.

Publication date:03/12/2007