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5.13 Pumpdown cycle
WARNING
Operation below atmospheric pressure! Fire hazard! During operation
below atmospheric pressure in A2L-refrigerant applications, a flammable
mixture can form inside the system. Ensure system tightness to prevent any
ingress of air. For further details see section 3.5 "System protection for
operation below atmospheric pressure".
CAUTION
Vacuum operation! Compressor damage! Compressor operation outside
the operating envelope is not allowed.
A pumpdown cycle to control refrigerant migration may have to be used for several reasons, for
example when the compressor is located outdoors without any housing so that cold air blowing over
the compressor makes the crankcase heater ineffective.
If a pumpdown cycle is used, a separate external check valve must be added. The scroll
discharge check valve is designed to stop extended reverse rotation and prevent high-pressure gas
from leaking rapidly into the low side after shut-off. The check valve might in some cases leak more
than reciprocating compressor discharge reeds, normally used with pumpdown, causing the scroll
compressor to recycle more frequently. Repeated short cycling of this nature can result in a low oil
situation and consequent damage to the compressor. The hysteresis of the low-pressure control
differential has to be reviewed since a relatively large volume of gas will re-expand from the high side
of the compressor into the low side after shutdown.
For pressure control setting, never set the low-pressure limiter to shut off outside of the
operating envelope. To prevent the compressor from running into problems during such
faults as loss of charge or partial blockage, the low-pressure limiter shall not be set lower
than the minimum suction pressure allowed by the operating envelope.
5.14 Minimum run time
Emerson recommends a maximum of 10 starts per hour. There is no minimum off time because
scroll compressors start unloaded, even if the system has unbalanced pressures. The most critical
consideration is the minimum run time required to return oil to the compressor after start-up. To
establish the minimum run time, a sample compressor equipped with an external oil sight glass is
available from Emerson. The minimum on time becomes the time required for oil lost during
compressor start-up to return to the compressor sump and to restore a minimal oil level that will
ensure oil pick-up through the crankshaft. Cycling the compressor for a shorter period than this, for
instance to maintain very tight temperature control, will result in progressive loss of oil and damage
to the compressor.
5.15 Sound characteristics
Copeland scroll digital compressors incorporate comparable sound characteristics as the fixed-
speed scroll models though the sound behaviour during capacity modulation is different. The
unloaded sound power is approximately 2 dB(A) higher than the loaded sound power. For noise-
sensible applications, an observation of the individual system sound characteristics, particularly
during the transition between loading and unloading state, is recommended. Depending on the
individual system properties, suitable noise reduction measures, for example the use of sound-
absorbing material, should be considered.
5.16 Shut-off sound
Scroll compressors incorporate a device that minimizes reverse rotation. The residual momentary
reversal of the scrolls at shut off could cause a clicking sound. It is entirely normal and has no effect
on compressor durability.
5.17 Supply frequency and voltage
There is no general release of Copeland digital scroll compressors for use with variable speed drives.
Only frequencies from 50 to 60 Hz are acceptable.
The last letter of the motor code indicates which frequency and voltage must be applied - see section
2.2 "Nomenclature".
AGL_Ref_DG_YBDK1E_EN_Rev04
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