JOHNSON CONTROLS
99
FORM 150.27-NM1
ISSUE DATE: 09/30/2015
7
SECTION 7 – 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 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 sta-
tus, and daily schedules. The MicroComputer Control
Center consists of four basic components:
1. IPU II and I/O Boards
2. Transformer
3. Display
4. Keypad.
The keypad allows programming and accessing set-
points, pressures, temperatures, cutouts, daily sched-
ule, options, and fault information.
Remote cycling, demand limiting and chilled liquid
temperature reset can be accomplished by field sup-
plied contacts.
Compressor starting/stopping and loading/unload-
ing decisions are performed by the microprocessor to
maintain leaving or return chilled liquid temperature.
These decisions are a function of temperature devia-
tion from setpoint.
A Master ON/OFF switch is available to activate orde-
activate the unit.
IPU II and I/O Boards
The IPU and I/O boards are assembled to function as
a single microprocessor controller requiring no addi-
tional hardware. The IPU II board contains a coldfire
microprocessor and is the controller and decision mak-
er in the control panel. The I/O board handles all the
chiller I/O (Inputs and Outputs). System inputs from
pressure transducers and temperature sensors are con-
nected to the I/O board. The I/O board contains a pro-
cessor capable of reading the inputs and controlling the
outputs. It communicates through the transition header
with the IPU II microprocessor.
The I/O board circuitry multiplexes the analog inputs,
digitizes them, and constantly scans them to keep watch
on the chiller operating conditions. The input values
are transmitted serially to the IPU II microprocessor
board. From this information, the IPU II then issues
commands to the I/O board relay outputs to control
contactors, solenoids, etc. for Chilled Liquid Tempera-
ture Control and to react to safety conditions. The I/O
board converts logic signals to operate relay outputs to
115 VAC levels used by motor contactors, fan contac-
tors, solenoid valves, etc. to control system operation.
The low voltage side of all relay coils on the I/O board
are powered by +12V.
Keypad commands are actuated upon by the micropro-
cessor to change setpoints, cutouts, scheduling, operat-
ing requirements, and to provide displays. The keypad
and display are connected to the I/O board.
LD15596
