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© 2012 Emerson Climate Technologies, Inc.
Printed in the U.S.A.
AE4-1395
Application Engineering
BULLETIN
Compressor operation during the loaded state should
always be inside of the envelope. The envelopes
represent allowable operation of the compressor with
20F°suctionsuperheatatratedvoltage.Ifthespecied
modulation ranges are exceeded, overheating of the
compressor and tripping of the overload can occur
because of inadequate motor cooling.
Solenoid Valve and Coil
The external solenoid valve and coil specied by
Emerson must be used since this is a critical component
for the proper functioning of this compressor. The
solenoid valve and coil are designed for approximately
32 million cycles. Do not attempt to substitute
replacement coils or valves; use only the replacement
parts specied in Table 4. Refer to the Service
Procedures section for information on changing the
modulation valves.
Pressure Fluctuations
During scroll modulation the suction and the discharge
pressure will uctuate. This uctuation should be
observed during unit testing. The installation and setting
of pressure controls should take this into account.
During the unloaded state, the discharge pressure will
decrease and the suction pressure will increase. This
normal pressure uctuation has had no observable
effect on the reliability of system components, however,
component manufacturers should be consulted to
ensure the proper application of their products.
Piping
Unlikeavariablespeedcompressorwhosemassow
and gas velocity changes with its speed, the digital
scroll’s pumping capacity is equal to its 100% capacity
while it is pumping. For this reason the gas velocity
remains high even during periods when the capacity
demandislow.Becausethemassowandgasvelocity
remain high, piping may be designed as if it were
designed for a non capacity controlled compressor. For
verticalpipingatrapevery20feetshouldbesufcient
to ensure proper oil return. This recommendation is
based upon a minimum 1500 fpm velocity or higher.
When the digital scroll compressor is part of a tandem,
a double riser should be considered to assure that the
velocity remains above 1500 fpm when only the digital
scroll is running.
Start Up and Shut Down
To improve the starting characteristics of the digital
scroll compressor, the the Emerson controllers delay
loading the compressor for 0.1 seconds. Likewise, to
eliminate the reverse rotation sound at shut down the
compressor is unloaded 0.5 seconds before shut down.
Compressor Cycling
Because of the digital scroll's seamless capacity
modulation from 10% to 100%, capacity short cycling
should not be a problem for single compressors.
However, if the digital compressor is in tandem with a
non modulated scroll, short cycling of the non modulated
compressor may be a problem if the system control is
not designed and set correctly. The Emerson digital
controllers have a built in two minute anti-short cycle
timer to prevent short cycling.
Sound Characteristics
The sound spectrum of the loaded state and the
unloaded state are different. Special consideration
should be given to the transition sound between the
loaded and unloaded states. If the transition sound
is unacceptable, a heavy sound blanket should
be applied to the compressor. Fabricating Services
(www.fabsrv.com) is a one source for scroll compressor
sound blankets.
The Emerson controllers unload the compressor a
fraction of a second before shut down allowing the scroll
set to unload, ensuring a relatively quiet shutdown.
Internal Pressure Relief (IPR) Valve
WARNING
A high pressure control must be used in all
ZRD94-125KC and ZPD103-182KC applications
because these compressors do not have internal
pressure relief (IPR) valves.
High Pressure Control
As mentioned above, not all digital scrolls have IPR
valves, therefore high pressure controls are required
in some applications. The recommended maximum cut
out setting is 425 psig (30 bar) for R-407C & R-22 and
650 psig (45 bar) for R-410A. The high pressure control
should have a manual reset feature for the highest
level of system protection. This pressure control must
act independently of the digital compressor controller.
Low Pressure Control
Air-conditioning units can be protected against high
discharge temperatures through a low pressure control in
the suction line. Testing has shown that a cut out setting
of not lower than 55 psig (3.8 bar) for R-410A and 25
psig (1.7 bar) for R-407C & R-22 will adequately protect
the compressor against overheating from loss of charge,
blower failure in a TXV system, etc. A higher level of
protection is achieved if the low pressure control is set to
cut out at 95 psig (6.7 bar) for R-410A and 55 psig (3.8