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© 2011 Emerson Climate Technologies
Printed in the U.S.A.
AE5-1377 R2
Application Engineering
BULLETIN
□ LED signal will display an Over Current Error
for 3 minutes
□ After a 3 minute delay the compressor will go
through a normal start
□ The system will lock out after 6 over current
trips within an hour
For this function to operate, two of the power leads are
routed through the current sensing coils (CT1, CT2),
prior to the contactor, from the factory. See Figure 3.
Non-Adjustable High Pressure Control
This pressure sensing device is a nonadjustable, low
voltage pressure switch that will open at 435psig and
reset at 348psig in the event of high discharge pressure.
Its signal is monitored by the control board.
• In the event of a high pressure trip, the unit will stop
and then restart after a 3-minute delay.
• After 6 successive HP cut-outs within 1 hour, the
unit will lock-out.
• The lockout feature can be reset by disconnecting
the power source and then cycling power to the unit.
Adjustable Low Pressure Switch
An adjustable low pressure switch is provided as
standard equipment on both the medium and low
temperature condensing units. This control can be
used for a pump-down cycle if so desired. See Table 8,
Low Pressure Control Settings (page 13). No error
message will be shown for this adjustable control.
Liquid Floodback Protection
• Liquid refrigerant entering the compressor during
the run cycle, in excessive quantities, can damage
the compressor by diluting the lubricant, as well
as excessive stress on several components in the
compressor. Proper control of liquid refrigerant
within the system is an application issue and is
beyond control of this controller. However, the
controller can perform checks and alert the user
that liquid refrigerant fl oodback may be occurring
and immediate fi eld service is required. This is
only a warning signal and will not terminate the
operation of the unit. See Tables 6 and 6a (page
13).
• Liquid Floodback Protection is acquired by
monitoring the compressor discharge temperature.
When the discharge line temperature falls below
a specifi ed point, low suction line superheat may
be the cause.
Crankcase Heater
The crankcase heater is wired through a normally closed
contact of the compressor contactor which is energized
whenever the compressor cycles off.
Condenser Fan Speed Control
The Condenser Fan Speed Control will vary the speed of
the condenser fan motor for head pressure control under
low ambient conditions. There are two thermistor type
sensors that are connected to the control board. These
sensors monitor the condenser mid coil temperatures
and ambient air temperatures to control the fan speed.
Enhanced Vapor Injection (EVI) Control (Low
temperature units only)
The EVI system improves low temperature operational
effi ciency and provides a reliable low temperature
envelope. It is used to optimize performance and to
prevent the scroll set from overheating. This is done by
controlling the discharge line temperature (DLT) and
vapor injection superheat (VISH).
Enhanced vapor injection is accomplished by utilizing a
subcooling circuit. A heat exchanger is used to subcool
the liquid refrigerant before it enters the evaporator. As
a result of the subcooling done by the heat exchanger,
refrigerant will also be evaporated. This evaporated
refrigerant is then injected into the mid compression
cycle of the scroll compressor for overheat temperature
control.
There are two thermistors sensing the discharge line
temperature, one is located at the discharge line of the
compressor and the second one is placed at the inlet of
the condenser coil. In order to have a higher temperature
resolution, the discharge line thermistor and condenser
coil inlet sensor cooperate to sense a temperature range
from 50°F to 329°F. The discharge line thermistor has a
sensing range from 163°F to 329°F and the condenser
coil will sense temperature from 50°F to 176°F. The EVI
system will keep the discharge line temperature below
230°F to ensure the safety of the compressor.
It is important to insulate the system liquid line from the
condensing unit to the evaporator. The recommended
insulation thickness is a minimum of ½ inch. Also the
lower liquid temperature can increase the evaporator
expansion valve capacities. Please follow the valve
manufactures recommended liquid temperature
correction factors for proper selection of the evaporator
expansion valve.
Electronic Expansion Value (EXV)
The Electronic Expansion Value (EXV) is a key part
of the EVI system. It will regulate vapor injection fl ow
to optimize the performance of system and cool the
scroll set. Every second, the control chip will collect the
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