Start-Up And Shut-Off Sound; Deep Vacuum Operation; Pumpdown Cycle - Emerson Copeland YB56K1G Application Manuallines

caused by operating three-phase Copeland scroll compressors in the reverse direction for a short
period of time (under one hour) but oil may be lost. Oil loss can be prevented during reverse rotation
if the tubing is routed at least 15 cm above the compressor. After several minutes of operation in
reverse, the compressor protection system will trip due to high motor temperature. The operator will
notice a lack of cooling. However, if allowed to repeatedly restart and run in reverse without correcting
the situation, the compressor will be permanently damaged.
All three-phase scroll compressors are identically wired internally. Therefore, once the correct
phasing is determined for a specific system or installation, connecting properly phased power leads
to the identified compressor terminals will ensure proper rotation direction.
5.9

Start-up and shut-off sound

During the very brief start-up, a clicking sound resulting from the initial contacting of the spirals is
audible; this sound is normal. Due to the design of the Copeland scroll compressors, the internal
compression components always start unloaded even if system pressures are not balanced. In
addition, since internal compressor pressures are always balanced at start-up, low-voltage starting
characteristics are excellent for Copeland scroll compressors.
Scroll compressors incorporate a device that minimizes reverse rotation. The residual momentary
reversal of the scrolls at shut-off will cause a clicking sound, but it is entirely normal too and it has no
effect on compressor durability.

5.10 Deep vacuum operation

CAUTION
Vacuum operation! Compressor damage! Copeland scroll compressors in
refrigeration or air-conditioning applications should never be used to evacuate
a system. Operating scroll compressors in deep vacuum could damage
internal motor parts and lead to unacceptable high temperatures in the
compressor housing.
For operation below atmospheric pressure with flammable refrigerants, see section 3.5 "System
protection for operation below atmospheric pressure".

5.11 Pumpdown cycle

WARNING
Operation below atmospheric pressure! Fire hazard! During operation of
A3-refrigerant systems below atmospheric pressure, 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,
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.
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