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YORK INTERNATIONAL
22
UNIT CONTROLS AND OPERATION
YORK MICROCOMPUTER CONTROL CENTER
FIG. 8 – MICROCOMPUTER CONTROL CENTER
26572A
INTRODUCTION
The YORK MicroComputer Control Center is a micro-
processor 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 setpoints, pres-
sures, temperatures, motor current, cutouts, daily sched-
ule, 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
decisions 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 deci-
sion maker in the control panel. System inputs from
pressure transducers, temperature sensors, and C.T.’s
are connected directly to the Microprocessor Board.
The Microprocessor Board circuitry multiplexes these
analog inputs, digitizes them, and constantly scans
them to keep a constant watch on the chiller operating
conditions. From this information, the Microprocessor
then issues commands to the Relay Output Board to
control contactors, solenoids, etc. for water tempera-
ture control 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.