York Millennium YCAJ150, Installation Operation & Maintenance, Page: 31 / 116

FORM 150.65-NM4
31 YORK INTERNATIONAL
UNIT CONTROLS AND OPERATION
YORK MILLENNIUM CONTROL CENTER
FIG. 9 – MILLENNIUM CONTROL CENTER
INTRODUCTION
The YORK Millennium Control Center is a microproces-
sor based control system capable of multi-circuit control
to maintain chilled liquid temperature.
A 40 character display (2 lines of 20 characters) allows
the operator to display system operating parameters as
well as access programmed information already in
memory. A keypad for programming and accessing set-
points, pressures, temperatures, motor current, cutouts,
daily schedule, options, and fault information is provided.
A master ON/OFF switch is available to activate or de-
activate the chiller system. Separate system (SYS)
switches for each refrigerant system (up to 4) are pro-
vided on the Microprocessor Board.
Remote cycling, unloading, and chilled water tempera-
ture reset can be accomplished by user supplied dry
contacts.
Compressor starting/stopping and loading/unloading de-
cisions are performed by the Microprocessor to main-
tain leaving water temperatures. These decisions are a
function of temperature deviation from setpoint and rate
of change of temperature.
MICROPROCESSOR BOARD
The Microprocessor Board is the controller and decision-
maker in the control panel. System inputs from pres-
sure transducers, temperature sensors, and C.T.s are
connected directly to the Microprocessor Board. The Mi-
croprocessor Board circuitry multiplexes these analog
inputs, digitizes them, and constantly scans them to
keep a constant watch on the chiller operating condi-
tions. From this information, the Microprocessor then
issues commands to the Relay Output Board to control
contactors, solenoids, etc. for water temperature con-
trol and to react to safety conditions.
Keypad commands are acted upon by the micro to
change setpoints, cut-outs, scheduling, operating re-
quirements, and to provide displays.
A +12V REG supply voltage from the Power Supply Board
is converted to +5V REG by a voltage regulator located
on the Microprocessor Board. This voltage is used to
operate integrated circuitry on the board.
Four system switches located on the Microprocessor
Board activate or deactivate the individual systems (com-
pressors).
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