YORK INTERNATIONAL
96
UNIT CONTROLS
YORK MILLENNIUM CONTROL CENTER
INTRODUCTION
The YORK MicroComputer Control Center is a micro-
processor based control system designed to provide the
entire control for the condensing unit. The control logic
embedded in the microprocessor based control system
will provide control for the discharge air temperature
or suction pressure, as well as sequencing, system safe-
ties, displaying status, and daily schedules. The
MicroComputer Control Center consists of four basic
components, 1) microprocessor board, 2) transformer,
3) display and 4) keypad. The keypad allows program-
ming and accessing setpoints, pressures, temperatures,
cutouts, daily schedule, options, and fault information.
Remote cycling, demand limiting and temperature re-
set can be accomplished by field supplied contacts.
Compressor starting/stopping and loading/unloading de-
cisions are performed by the Microprocessor to main-
tain either the discharge air temperature or system suc-
tion pressure. These decisions are a function of tem-
perature or system suction pressure deviation from set-
point.
A Master ON/Off switch is available to activate or de-
activate the unit.
Unit Controls
00065VIP
MICROPROCESSOR BOARD
The Microprocessor Board is the controller and deci-
sion maker in the control panel. System inputs such as
pressure transducers and temperature sensors are con-
nected directly to the Microprocessor Board. The Mi-
croprocessor Board circuitry multiplexes the analog in-
puts, digitizes them, and scans them to keep a constant
watch on the unit operating conditions. From this in-
formation, the Microprocessor then issues commands
to the Relay Outputs to control contactors and sole-
noids for discharge air temperature or system suction
pressure control, and to react to safety conditions.
Keypad commands are acted upon by the micro to
change setpoints, cutouts, scheduling, operating require-
ments, and to provide displays.
The on-board power supply converts 24VAC from the
1T transformer to a +12 VDC and +5 VDC regulated
supply located on the Microprocessor Board. This volt-
age is used to operate integrated circuitry on the board.
The 40 character display and unit sensors are supplied
power from the micro board 5 VDC supply.
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