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6.5
Exchanging the refrigerant
WARNING
Air/A2L mixture! Flammable and explosive atmosphere! Fire and
explosion hazard! In any case avoid air/A2L mixture in the refrigeration
system. Make sure that the system is filled with pure A2L refrigerant. In the
event that the refrigerant needs replacing, the charge should be recovered
using A2L qualified refrigerant recovery unit and recycling bottles.
CAUTION
Low suction pressure operation! Compressor damage! Do not operate
with a restricted suction. Do not operate with the low-pressure limiter bridged.
Do not operate compressor at pressures that are not allowed by the operating
envelope. Allowing the suction pressure to drop below the envelope limit for
more than a few seconds may overheat scrolls and cause early drive bearing
and moving parts damage.
For qualified refrigerant and oil, see Chapter 2.4.1.
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 shutdown
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.
6.6
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.
6.6.1 Compressor replacement
In the case of A2L refrigerant compressor replacement, the oil has to be drained out of the
compressor and the compressor should be flushed with dry nitrogen. DO NOT close the stubs with
plugs.
In the case of a motor burnout, the majority of contaminated oil will be removed with the compressor.
The rest of the oil will be 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 compressor 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.
6.6.2 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.
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