Emerson COPELAND ZO18AG, Инструкции по применению

Страница: 31 / 38

26 AGL_Ref_ST_ZO_E_Rev00
6.5 Replacing a compressor
CAUTION
Inadequate lubrication! Bearing destruction!
For systems with refrigerant
accumulator, exchange the accumulator after replacing a compressor with a
burned-out motor. The accumulator oil return orifice or screen may be plugged
with debris or may become plugged. This will result in starvation of oil to the
new compressor and a second failure.
Remove the refrigerant and oil completely from the replaced compressor.
6.5.1 Compressor replacement
In the case of a motor burnout, the majority of contaminated oil will be removed with the compressor.
The rest of the oil is cleaned through the use of suction and liquid line filter driers. A 100 % activated
alumina suction line filter drier is recommended but must be removed after 72 hours. When a single
compressor or tandem is exchanged in the field, it is possible that a major portion of the oil may still
be in the system. While this may not affect the reliability of the replacement compressor, the extra oil
will add to rotor drag and increase power usage.
6.5.2 Start-up of a new or replacement compressor
Rapid charging only on the suction side of a scroll-equipped system can occasionally result in a
temporary no-start condition for the compressor. The reason for this is that, if the flanks of the scrolls
happen to be in a sealed position, rapid pressurisation of the low side without opposing high-side
pressure can cause the scrolls to seal axially. As a result, until the pressures eventually equalise,
the scrolls can be held tightly together preventing rotation. The best way to avoid this situation is to
charge on both the high and low sides simultaneously at a rate which does not result in axial loading
of the scrolls.
A minimum suction pressure specified in the published operating envelope must be maintained
during charging. Allowing the suction pressure to drop below that value may overheat the scrolls and
cause early drive bearing and moving parts damage. Never install a system in the field and leave it
unattended when it has no charge, a holding charge, or with the service valves closed without
securely electrically locking out the system. This will prevent unauthorised personnel from
accidentally operating the system and potentially ruining the compressor by operating with no
refrigerant.
Do not start the compressor while the system is in a deep vacuum. Internal arcing
may occur when a scroll compressor is started in a vacuum causing burnout of the internal lead
connections.
6.6 Lubrication and oil removal
The compressor is supplied with an initial oil charge. The standard oil for use with R744 is a
polyalkylene glycol oil (PAG) lubricant ZEROL RFL68-EP. See nameplate for original oil charge
shown in litres.
One disadvantage of PAG is that it is far more hygroscopic than mineral oil
– see
Figure 23 . Only
brief exposure to ambient air is needed for PAG to absorb sufficient moisture to make it unacceptable
for use in a refrigeration system. Since PAG holds moisture more readily than mineral oil it is more
difficult 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. Therefore, it is
recommended that a properly sized filter-drier be installed in all PAG 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
PAG with a moisture content no higher than 50 ppm.
Figure 23: Absorption of moisture in PAG oil in comparison to mineral oil in ppm by weight at 25 °C and 50 %
relative humidity (h= hours)