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6
Maintenance & repair
6.1
Exchanging the refrigerant
Qualified refrigerants and oils are given in section 2.3.1.
It is not necessary to replace the refrigerant with new unless contamination due to an error such as
topping up the system with an incorrect refrigerant is suspected. To verify correct refrigerant
composition, a sample can be taken for chemical analysis. A check can be made during shut down
by comparing the refrigerant temperature and pressure using precision measurements at a location
in the system where liquid and vapour phases are present and when the temperatures have
stabilised.
In the event that the refrigerant needs replacing, the charge should be recovered using a suitable
recovery unit.
6.2
Replacing a compressor
CAUTION
Inadequate lubrication! Bearing destruction! 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.
6.2.1 Compressor replacement
When a compressor is exchanged in the field, a major portion of the oil may remain 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. The compressor should be run for 10 minutes, shut down and the
extra oil removed via the Schraeder valve when fitted (only ZBH). This operation should be repeated
at least twice to make sure the proper oil level is achieved. The oil level should be maintained halfway
up the sight glass.
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. It is highly
recommended that the suction accumulator be replaced if the system contains one. This is
because the accumulator oil-return orifice or screen may be plugged with debris or may become
plugged shortly after a compressor failure. This will result in starvation of oil to the replacement
compressor and a second failure. 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.
6.2.2 Start-up of a new or replacement compressor
Rapid charging only on the suction side of a scroll-equipped system or condensing unit can
occasionally result in a temporary no start condition for the compressor. The reason for this is that,
if the flanks of the compressor 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 of 1.75 bar must be maintained during charging. Allowing pressure to
drop below 0.5 bar for more than a few seconds may overheat scrolls and cause early drive bearing
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 flow. 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.
C6.2.7/1007-0619/E
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