York YCAS0295EB, Installation Operation & Maintenance

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15 YORK INTERNATIONAL
FORM 201.19-NM7 (804)
Each power compartment contains:
Compressor and fan starting contactors, fan motor
ex ter nal overloads, control circuit serving compressor
ca pac i ty control, compressor and fan contactor coils and
compressor motor overloads. (Fig 1, page 12)
Current transformers in the 2ACE module provide
compressor motor over load protection and sense each
phase. This protects the compressor motors from
dam age due to: low current input, high input current,
un bal anced current, single phasing, phase reversal, and
com pres sor locked rotor.
The control section contains:
ON/OFF switch, microcomputer keypad and display,
mi cro pro ces sor 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 con trol
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-
vid ed on two lines and light emitting diode back-
light ing out door viewing.
• A color coded, 35 button, sealed keypad with sec-
tions for Display, Entry, Setpoints, Clock, Print,
Pro gram and Unit ON/OFF.
The standard controls shall include: brine chilling,
ther mal storage, automatic pump down, run signal
con tacts, demand load limit from external building
automation sys tem input, remote reset liquid temperature
reset in put, unit alarm contacts, chilled liquid pump
control, au to mat ic reset after power failure, automatic
system op ti mi za tion to match operating conditions.
The software is stored in non-volatile memory (EPROM)
to eliminate chiller failure due to AC power failure. The
Programmed Setpoints are 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 ac com plished by sending a current signal pro por tion al
to motor current from the Motor Protector mod ule to the
I/O Expansion board to be multiplexed and sent to the
Microprocessor Board. If the motor cur rent exceeds
the 115% FLA trip point after 3 seconds of op er a tion
on either Wye-Delta or ACL starters, the mi cro will
shut the system down and lock it out after one fault.
A manual reset of the re spec tive system switch is
re quired to clear the fault and restart the system. A
thor ough check of the mo tor, wiring, and refrigerant
system should be done be fore restarting a system that
has fault ed 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
pro tec tion is activated 4 seconds after start on both
Wye-Delta and ACL starters to assure the motor starts,
the sys tem doesn’t run with out refrigerant, the motor
protector is not tripped, and the mechanical high pres sure
cut-out is not tripped. Once the system is locked out
on Low Motor Current, it must be manually reset with
the sys tem 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 mo tor
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.
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