FORM 150.66-NM2
ISSUE DATE: 09/25/2020
99
JOHNSON CONTROLS
7
SECTION 7 - UNIT CONTROLS
YORK
MILLENNIUM
CONTROL CENTER
The YORK MicroComputer Control Center is a
microprocessor based control system designed to provide
the entire control for the liquid chiller. The control logic
embedded in the microprocessor based control system
will provide control for the chilled liquid temperatures,
as well as sequencing, system safeties, 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 programming and accessing setpoints,
pressures, temperatures, cutouts, daily schedule, options,
and fault information.
Remote cycling, demand limiting and chilled liquid
temperature reset can be accomplished by field supplied
contacts.
Compressor starting/stopping and loading/unloading
decisions are performed by the Microprocessor to
maintain leaving or return chilled liquid temperature.
These decisions are a function of temperature deviation
from setpoint.
A Master ON/Off switch is available to activate or
deactivate the unit.
INTRODUCTION
MICROPROCESSOR BOARD
The Microprocessor Board is the controller and
decision maker in the control panel. System inputs
such as pressure transducers and temperature sensors
are connected directly to the Microprocessor Board.
The Microprocessor Board circuitry multiplexes the
analog inputs, digitizes them, and scans them to keep
a constant watch on the chiller operating conditions.
From this information, the Microprocessor then issues
commands to the Relay Outputs to control contactors,
solenoids, etc. for Chilled Liquid Temperature Control
and to react to safety conditions.
Keypad commands are acted upon by the micro to change
setpoints, cutouts, scheduling, operating requirements,
and to provide displays.
The on-board power supply converts 24 VAC from the
1T transformer to a +12 VDC and +5 VDC regulated
supply located on the Microprocessor Board. This
voltage is used to operate integrated circuitry on the
board. The 40 character display and unit sensors are
supplied power from the microboard 5 VDC supply.
24 VAC is rectified and filtered to provide unregulated
+30 VDC to supply the flow switch, PWM remote
temperature reset, and demand limit circuitry which is
available to be used with field supplied contacts. The
Microprocessor Board energizes on-board relays to
output 120 VAC to motor contactors, solenoid valves,
etc. to control system operation. 120 VAC is supplied
to the optimal T3 Transformer, which supplies 12 VAC
to the bridge diode module. The Bridge Diode Module
rectifies the voltage to -12 V unreg. The +12 V unreg
voltage supplies power to the Remote Temp. Reset
Circuit Board.
00065VIP
Summary of Contents for YCAL0012EC
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