Dunham-Bush ACXi 165-5SP-LN, Installation, Operation And Maintenance Manual

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4.0 ELECTRICAL
4.5.10 Chilled Water Reset and
Customer Control Interlock
(Optional)
The chilled water temperature setpoint
can be raised automatically by a 0-5
VDC signal provided by an external
controller. The reset signal must be
between 0VDC and 5VDC, with 0VDC
being no reset and 5VDC being max.
reset. The maximum temperature reset
(increase) desired must be stored in
CWR max. B setpoint. For example, to
raise the chilled water setpoint from
44°F to 50°F (6.0°F) with a 5VDC input,
a 6.0 is stored in CWR max. setpoint.
Control contacts from an external
controller can be used enable or disable
operation of compressors. The wiring
diagram specifies the terminals to which
the contacts must to be wired. To enable
the compressors, the contacts must he
closed. To disable the compressors, the
contacts must be opened.
4.5.11 Variable Fan Speed Control
(Optional)
When variable fan speed control has
been applied with the package, an output
from the computer controls the Variable
Speed Drive (VFD). The VFD is turned
on to maintain the set discharge pressure.
Fan speed increases as discharge
pressure rises and decreases as discharge
pressure drop. Refer VFD manual for
drive operation.
4.5.12 Sump Heater Control
Each compressor is fitted with an oil
sump band-heater. The heater is
energized at all times when compressor
is off and de-energized when the
compressor is running.
Its purpose is to prevent refrigerant
migration into the oil during shut down.
For this reason, it is essential that heaters
be energized for 24 hours before starting
a compressor.
4.6 SAFETY FUNCTlONS
4.6.1 Control Power Loss
(Microcomputer)
The microcomputer can be set up to start
automatically or manually after a power
failure to the microcomputer. The power
loss B setpoint is factory set to 0.0 to
allow automatic start after a control
power loss. To select manual reset, set
power loss B setpoint to 1.0. In this case,
a power loss alarm will be stored by the
microcomputer and RESET must be
pressed to start.
4.6.2 Low Pressure Cut-off
(Microcomputer)
This function protects the unit from
operating at abnormally low evaporator
refrigerant pressure. The microcomputer
will shut down the compressor when
Evaporator pressure falls below the low
pressure setpoint and turn on the alarm
pilot light.
A low pressure alarm will be recorded by
the microcomputer. Reset by pressing
the RESET button on the micro-
computer. Standard setpoint is 45 psig
for water systems.
4.6.3 Evaporator Freeze Shutoff
(Microcomputer)
If the leaving chilled water temperature
drops below the freeze setpoint, the
microcomputer will shut down the unit
and store the freeze alarm. After solving
the problem, press RESET on the
microcomputer to clear the alarm.
4.6.4 High Pressure Cut-off
(Microcomputer)
This function protects the compressor
from operating at abnormally high
discharge refrigerant pressures. The
microcomputer will shut down the
compressor when condenser pressure
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