AE4-1312 R2
© 2010 Emerson Climate Technologies
Printed in the U.S.A.
5
Single Phase Starting Characteristics
Start assist devices are usually not required, even if
a system utilizes non-bleed expansion valves. Due to
the inherent design of the Copeland Scroll, the internal
compression components always start unloaded even
if system pressures are not balanced. In addition, since
internal compressor pressures are always balanced at
startup, low voltage starting characteristics are excellent
for Copeland Scroll compressors. Starting current on
any
compressor may result in a significant “sag” in
voltage where a poor power supply is encountered. The
low starting voltage reduces the starting torque of the
compressor and subsequently increases the start time.
This could cause light dimming or a buzzing noise where
wire is pulled through conduit. The start components
listed in
Table 7
will substantially reduce start time and
consequently the magnitude and duration of both light
dimming and conduit buzzing.
PTC Start Components
For less severe voltage drops or as a start boost, solid
state Positive Temperature Coefficient devices rated
from 10 to 25 ohms may be used to facilitate starting
for any of these compressors.
Electrical Connection
The orientation of the electrical connections on the
Copeland Scroll compressors is shown in
Figure 4.
Three electrical connection options are available for
these compressors. These include the “Molded Plug”
one piece push-on connection, available in certain
markets, and “Quick Connect” flag termination available
on all scrolls of this size. Some four-ton and larger
models also offer “T-block Screw Connection” for ring
termination.
Deep Vacuum Operation
Scrolls incorporate internal low vacuum protection
and will stop pumping (unload) when the pressure
ratio exceeds approximately 10:1. There is an audible
increase in sound when the scrolls start unloading.
Copeland Scroll compressors
(as with any refrigerant
compressor)
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 shown in
Figure 5.
Prolonged operation at
low suction pressures will result in overheating of the
scrolls and permanent damage to the scroll tips, drive
bearings and internal seal. (See
AE24-1105
for proper
system evacuation procedures.)
Nomenclature
The model numbers of the Copeland Scroll compressors
include the approximate nominal 60 HZ capacity at
standard operating conditions. An example would be the
ZR24K3-TFD, which has 24,500 Btu/hr (7 kw) cooling
capacity at the ARI high temperature air conditioning
rating point when operated on 60 Hz. Note that the
same compressor will have approximately 5/6 of this
capacity or 20,200 Btu/hr (5.9 kw) when operated on 50
Hz current. Please refer to Online Product Information
at www.emersonclimate.com for details.
Shell Temperature
Certain types of system failures, such as condenser
or evaporator fan blockage or loss of charge, may
cause the top shell and discharge line to briefly but
repeatedly reach temperatures above 350ºF (177ºC)
as the compressor cycles on its internal protection
devices. Care must be taken to ensure that wiring or
other materials, which could be damaged
by these
temperatures, do not come in contact with these
potentially hot areas.
Suction and Discharge Fittings
Copeland Scroll compressors have copper plated steel
suction and discharge fittings. These fittings are far
more rugged and less prone to leaks than copper fittings
used on other compressors. Due to the different thermal
properties of steel and copper, brazing procedures may
have to be changed from those commonly
used. See
Figure 6
for assembly line and field brazing procedures.
Three Phase Scroll Compressors
Scroll compressors, like several other types of
compressors, will only compress in one rotational
direction. Direction of rotation is not an issue with
single phase compressors since they will always start
and run in the proper direction (except as described in
the section “Brief Power Interruptions”). Three phase
compressors will rotate in either direction depending
upon 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 is achieved when the system
is installed and operated.
Verification of proper
rotation direction is made by observing that suction
pressure drops and discharge pressure rises when the
compressor is energized. Reverse rotation will result
in substantially-reduced current draw compared to
normal values.
