Refrigerant Oil is a necessary component in any air conditioning system that uses compressor in its compression system. There are three main purposes of the oil. They are used for lubrication, removal of heat and for sealing.
Lubrication cooling is needed in reciprocating compressor as the piston compresses the refrigerant gas. The sealing of the piston in the cylinder needs to be cooled as well.
Similarly, rotary compressor needs lubrication for the contact between the cylinder and the rotor of the motor. Screw compressor superheat has to be removed by the lubricant during its operation.
Typical Compressor Oil & Refrigerants
The two categories of oils commonly used in the compressors are mineral or synthetic oils.
One type of mineral oil (MO) called Naphthenic is commonly used.
Synthetic oils such as glycols, esters and alkylbenzenes (AB) have been used in the refrigeration applications for some time without any problem.
CFC refrigerants such as R12, R13, R113, R114 and R115 are using mineral oil or alkylbenze as their lubricants. Similarly, HCFC refrigerants such as R22, R123, R401A and R409A are also using these lubricants in their design.
In recent years CFC and HCFC refrigerants usage began to dwindle due to their ozone-unfriendly properties. Usage of new HFC refrigerants such as R23, R32, R134a, R407A, R407C and R410A have been increasing in HVAC equipment. These new refrigerants use Polyol esters or POE as lubricant.
One setback of POE is that it absorbs moisture many times more compared to mineral based oils. Hence proper procedures must be used when handling this oil to reduce the contact of this oil with the atmosphere. Metal containers are used instead of plastic containers to prevent moisture from entering the containers.