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f or use in a ref rigeration system. Since POE holds moisture more readily than mineral oil it is more
dif ficult to remove it through the use of vacuum. The compressors supplied by Emerson contain oil
with low moisture content, which may rise during the system assembling process. Theref ore, it is
recommended that a properly sized filter-drier be installed in all POE systems. This will maintain the
moisture level in the oil to less than 50 ppm. If oil is charged into a system, it is recommended to use
POE with a moisture content no higher than 50 ppm.
Figure 18: Absorption of moisture in ester oil in comparison to mineral oil in ppm by weight at 25 °C and 50 % relative
humidity (h= hours)
If the moisture content of the oil in a ref rigeration system reaches unacceptably high levels, corrosion
and copper plating may occur. The system should be evacuated down to 0.3 mbar or lower. If there
is uncertainty as to the moisture content in the system, an oil sample should be taken and tested for
moisture. Sight glass/moisture indicators currently available can be used with the HFC ref rigerants
and lubricants; however, the moisture indicator will just show the moisture content of the refrigerant.
The actual moisture level of POE would be higher than the sight glass indicates. This is due to the
high hygroscopicity of the POE oil. To determine the actual moisture content of the lubricant, samples
have to be taken from the system and analysed.
6.7
Oil additives
Although Emerson cannot comment on any specific product, f rom our own testing and past
experience, we do not recommend the use of any additives to reduce compressor bearing losses or
f or any other purpose. Furthermore, the long-term chemical stability of any additive in the presence
of ref rigerant, low and high temperatures, and materials commonly found in ref rigeration systems is
complex and difficult to evaluate without rigorously controlled chemical laboratory testing. The use
of additives without adequate testing may result in malfunction or premature f ailure of components
in the system and, in specific cases, in voiding the warranty on the component.
