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5.9
Rotation direction
IMPORTANT
Insufficient internal lubrication! Bearing malfunction! Do not operate
YRH(V)*KTE/KTG horizontal scroll compressors in reverse rotation. Make sure
to electrically connect in the right rotating field and check the running
compressor for proper rotation direction.
The lubrication in YRH(V)*KTE/KTG horizontal scroll compressors will only work properly if
compressors run in the correct rotation direction. Three-phase compressors will rotate in either
direction depending upon the phasing of the power. Since there is a 50-50 chance of connecting
power in such a way as to cause rotation in the reverse direction, it is important to include notices
and instructions in appropriate locations on the equipment to ensure proper rotation direction
when the system is operated and serviced. Observing that suction pressure drops and discharge
pressure rises when the compressor is energized allows verification of proper rotation direction.
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.
Shell temperature
5.10
During normal operation, the discharge gas as well as the compressor top shell and discharge line
can reach temperatures up to the maximum discharge gas temperature of 120 °C – see section 3.7
"Discharge gas temperature protection".
In a failure mode, the discharge gas temperatures can even get higher. Care must be taken to ensure
that wiring or other materials that could be damaged by these temperatures do not touch the shell.
5.11 Refrigerant migration
Liquid migration to the compressor and consequent flooded starts after standstill, especially in a cold
ambient, must be avoided.
In mobile applications, a crankcase heater might not be effective due to lack of power. This could
lead to situations where there will be no voltage present during extended off-cycle periods. A
pumpdown cycle in combination with a low leak check valve in the discharge line could be an
alternative to reduce off-cycle refrigerant migration to the compressor. This extra low leak check
valve must be qualified for discharge line service.
For further support, please contact the Application Engineering department at Emerson or your local
Emerson representative.
5.12 Pumpdown cycle
WARNING
Operation below atmospheric pressure! Fire hazard! For applications with
A2L or A3 refrigerants, a flammable mixture can form inside the system during
operation below atmospheric pressure. 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.
The system can be set to pump down for a fixed number of seconds after the setpoint is reached
and the liquid line solenoid valve and/or the expansion valve is closed. The exact time should be
determined by testing but should not exceed 20 seconds. The system should pump down until the
pressure is close to the cut-out pressure of the low-pressure switch. It is not necessary to pump down
to pressure values lower than the low-pressure switch cut-out setpoint. If the low-pressure switch
opens, the pumpdown should stop immediately. The system should not restart when the low-
pressure switch resets; restart should be in response to controller demand. In heat pumps the 4-way
valve should not be allowed to shift after pumpdown.
If a pumpdown cycle is used, a separate external check valve must be added. The scroll
discharge check valve is designed to prevent rapid pressure equalisation, but it is not entirely gas-
tight. The check valve might in some cases leak, causing the scroll compressor to recycle more
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AGL_AC_ST_YRH_EN_Rev01
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