Refrigeration systems which contain Polyol Ester (POE) oil present technicians with additional concerns that are not normally an issue with systems using either mineral based or alkylbenzene oils.  Refrigeration technicians need to be aware of these issues while servicing and installing these systems, otherwise additional system problems can easily develop.

According to RHVACTools, one major concern when working with POE oils is that they are hygroscopic.  If they remain in contact with air, they have the ability to readily absorb moisture. For a technician this means when a repair requires opening a system, it should be left exposed to the atmosphere only as long as necessary to complete the repair. Also, when adding POE oil to a system be sure to tightly seal the container of the unused oil so that it does not take on moisture.  If unused oil does need to be stored, it should be in its original metal container rather than a plastic container, as POE oil can absorb moisture through the walls of traditional plastic.

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 and can release debris which 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 on the inside of the copper tubing. If brazed without the use of nitrogen, the oxide scale formed on the inner tubing can be scrubbed from the walls by the POE oil and travel throughout the system. Also, 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.