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The Power and Control Panel are divided into power
sections for each compressor and associated fans, a con-
trol section and an electrical options section. The power
and control sections have separate hinged, latched, and
gasket sealed doors equipped with wind struts.
Each power compartment contains:
Compressor and fan starting contactors, fan motor
external overloads, control circuit serving compressor
capacity control, compressor and fan contactor coils and
compressor motor overloads.
The current transformers for the compressor motor
overloads sense each phase, as an input to the micro-
processor. This protects the compressor motors from
damage due to: low current input, high input current,
unbalanced current, single phasing, phase reversal, and
compressor locked rotor.
The control section contains:
ON/OFF switch, microcomputer keypad and display,
microprocessor board, I/O expansion board, relay boards
and power supply board.
The options sections contain:
A control circuit transformer complete with service
switch providing 115/1/60 Hz power to the unit control
system.
Electrical options as described in "Accessories and
Options."
Microprocessor Controls
The microprocessor has the following functions and
displays:
• A liquid crystal 40 character display with text pro-
vided on two lines and light emitting diode back-
lighting outdoor viewing.
• A color coded, 35 button, sealed keypad with sec-
tions for Display, Entry, Setpoints, Clock, Print,
Program and Unit ON/OFF.
The standard controls shall include: brine chilling, ther-
mal storage, automatic pump down, run signal contacts,
demand load limit from external building automation
system input, remote reset liquid temperature reset
input, unit alarm contacts, chilled liquid pump control,
automatic reset after power failure, automatic system
optimization to match operating conditions.
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The software is stored in non-volatile memory (EPROM)
to eliminate chiller failure due to AC power failure.
The Programmed Setpoint is stored in lithium battery
backed memory.
Motor Current Protection
The microprocessor motor protection provides high cur-
rent protection to assure that the motor is not damaged
due to voltage, excess refrigerant, or other problems that
could cause excessive motor current. This is accom-
plished by sending 3-phase current signals proportional
to motor current from the Motor Protector module to the
Power Supply Board where the signals are conditioned
and routed to the I/O Expansion board to be multi-
plexed and sent to the Microprocessor Board. If the
motor current exceeds the 115% FLA trip point after
3 seconds of operation on either Wye-Delta or ACL
starters, the micro will shut the system down and lock
it out after one fault. A manual reset of the respective
system switch is required to clear the fault and restart
the system. A thorough check of the motor, wiring, and
refrigerant system should be done before restarting a
system that has faulted on high motor current.
The micro also provides low motor current protection
when it senses a motor current less than 10% FLA. The
micro will shut the system down whenever low motor
current is sensed and will lock out a system if three faults
occur in 90 minutes. Low motor current protection is ac-
tivated 4 seconds after start on both Wye-Delta and ACL
starters to assure the motor starts, the system doesn't run
without refrigerant, the motor protector is not tripped,
and the mechanical high pressure cut-out is not tripped.
Once the system is locked out on Low Motor Current,
it must be manually reset with the system switch. See
also Motor Protection Module section below.
The micro senses low motor current whenever a HPCO
or Motor Protector contact opens. This occurs because
the MP and HPCO contacts are in series with the motor
contactor. Whenever either of these devices are open,
the contactor de-energizes and the motor shuts down.
Since the micro is sending a run signal to the contactor,
it senses the low motor current below 10% FLA and
shuts the system down.
JOHNSON CONTROLS
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