26
D6.3.4/0715-0716/E
One disadvantage of POE is that it is far more hygroscopic than mineral oil (see
Figure 24
).
Only brief exposure to ambient air is needed for POE to absorb sufficient moisture to make it
unacceptable for use in a refrigeration system. Since POE holds moisture more readily than
mineral oil it is more difficult to remove it through the use of vacuum. Compressors supplied by
Emerson Climate Technologies contain oil with low moisture content, and it may rise during the
system assembling process. Therefore it is recommended that a properly sized filter-drier is
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 moisture content no higher than
50 ppm.
The diagram below compares the hygroscopic characteristics of POE oil with mineral oil
(moisture absorption in PPM at 25°C and 50% relative humidity).
Figure 24: 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 refrigeration system reaches unacceptable 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 refrigerants and lubricants; however, the moisture indicator will just show the
moisture contents 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.
6.6
Oil additives
Although Emerson Climate Technologies cannot comment on any specific product, from our own
testing and past experience, we do not recommend the use of any additives to reduce
compressor bearing losses or for any other purpose. Furthermore, the long term chemical
stability of any additive in the presence of refrigerant, low and high temperatures, and materials
commonly found in refrigeration 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 failure of components in the system and, in specific cases, in voiding
the warranty on the component.
6.7 Unbrazing system components
WARNING
Explosive flame! Burning!
Oil-refrigerant mixtures are highly flammable.
Remove all refrigerant before opening the system. Avoid working with an
unshielded flame in a refrigerant charged system.
Before opening up a system it is important to remove all refrigerant from both the high and low
sides of the system. If a brazing torch is then applied to the low side while the low side shell and
suction line contain pressure, the pressurized refrigerant and oil mixture could ignite when it
escapes and contacts the brazing flame. To prevent this occurrence, it is important to check both
the high and low sides with manifold gauges before unbrazing. Instructions should be provided in
appropriate product literature and assembly (line repair) areas. If compressor removal is
required, the compressor should be cut out of system rather than unbrazed.
