1
2
3
CC-000118
1
2
3
outlet
Inlet
Orifice
for oil return
Figure 21: Suction accumulator
Manage
off
cycle migration
General information
Off
-cycle refrigerant migration happens:
• When the compressor is located at the coldest part of the installation, refrigerant vapour condenses in the
compressor.
• Directly in liquid-phase by gravity or pressure
difference.
• Refrigerant migrates to evaporator during
off
cycle
Poor lubrication when a compressor starts can reduce compressor bearing life. The oil can be diluted by liquid
refrigerant that migrates to the crankcase in the
off-cycle,
or liquid refrigerant stored in evaporator slugging the
compressor when it
first
re-starts. In extreme situations, this leads to liquid slugging that can damage the
compressor scroll set.
Compressor charge limit
If the charge limit is exceeded, protective measures must be taken to limit the risk of liquid slugging and extreme
dilution at start.
Table 22: Compressor charge limit
Compressor model
Refrigerant charge limit
Kg
lb
VCH115
13
29
Test and components required per application
Table 23: Test and components required per application
Application
Components required
Non
Split
(1)
Split
Below
charge
limit
Above
charge
limit
Belt sump heater
Non return valve
Comments
X
X
Mandatory
Mandatory for unit with
water condenser (W/W
or reversible A/C Chiller)
Ensure tightness between condenser & evaporator when system is OFF
• If thermostatic expansion valve (TXV): Liquid line solenoid valve LLSV
strongly recommended, if not possible Suction accumulator can be used
as an alternative Bleed type valve not accepted
• If electronic expansion valve (EXV): must close when the system stops,
including in power shut down situation or power loss
X
X
Mandatory
Mandatory
X
Mandatory
Mandatory
(1)
Unit pre charge at OEM factory, no refrigerant piping done on
field
(1)
Unit pre charge at OEM factory, no refrigerant piping done on
field
To avoid condensed liquid refrigerant from draining back when the compressor is shut
off,
the condenser outlet
must have an “upper loop” shape.
Scroll compressors, VCH115 | Application
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