© 2017 Emerson Climate Technologies, Inc.
7
AE4-1372 R4
Operating Envelope
at the end of this bulletin shows the CO
2
cascade operating envelope in relation to R-410A and R-
404A.
Charging Procedure
Do not operate compressor without enough system
charge to maintain at least 87 PSIG (6 Bar) suction
pressure.
Do not operate with a restricted suction.
Do not operate with the low-pressure cut-out bridged.
Vapor initial charge should be 145 PSIG (10 Bar). Do
not allow a pressure under 87 PSIG (6 Bar), otherwise
it might cause CO
2
solidification and blocked valves or
pipes and consequently, the scrolls may overheat and
cause early drive bearing damage.
Do not use the compressor to test the opening set point
of the high-pressure cut-out. Bearings are susceptible to
damage before they have had several hours of normal
running in. Ensure charging equipment is approved for
at least 1300 PSIG (89.6 Bar).
The system should be charged through the liquid-
receiver shut-off valve or through a valve in the liquid
line.
The use of a filter drier in the charging line is
highly recommended.
Because there may be several valves in the system it is
recommended to charge on both the high and low sides
simultaneously to ensure a positive refrigerant pressure
is present in the compressor before it runs. The majority
of the charge should be placed in the high side of the
system to prevent bearing washout during first-time
start.
Deep Vacuum Operation
Copeland Scroll compressors should never be used to
evacuate a refrigeration or air-conditioning system. The
scroll compressor can be used to pump down refrigerant
in a unit as long as the pressures remain within the
operating envelope. Low suction pressures will result in
overheating of the scrolls and permanent damage to the
compressor drive bearing. ZO scrolls incorporate
internal low vacuum protection, the floating seal unloads
when the pressure ratio exceeds approximately 10:1.
Shell Temperature
The top shell and discharge line can briefly but
repeatedly reach temperatures above 350°F (176.7 °C)
if the compressor cycles on its internal protection
devices. This only happens under rare circumstances
and can be caused by the failure of system components
such as the condenser or evaporator fan or loss of
charge and depends upon the type of expansion control.
Care must be taken to ensure that wiring or other
materials that could be damaged by these temperatures
do not come in contact with the shell.
Pump Down Cycle and Parallel Rack Application
A pump down cycle for control of refrigerant migration
may be used in conjunction with a crankcase heater
when the compressor is located so that cold air blowing
over the compressor makes the crankcase heater
ineffective.
If a pump down cycle is used on a parallel rack system,
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-
down. The check valve will in some cases leak more
than reciprocating compressor discharge reeds,
normally used with pump down, 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 low-
pressure control differential must be reviewed since a
relatively large volume of gas will re-expand from the
high side of the compressor into the low side on
shutdown.
Low Pressure Safety Control
Never set the low-pressure control 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 control should not be set
lower than -60°F (-51.1°C) equivalent suction pressure
(80 PSIG, 5.51 bar) below the lowest design operating
point.
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, obtain a sample compressor equipped with a sight
