Johnson Controls York YCAL0014E Series, Installation, Operation & Maintenance Instructions Manual

Page: 70 / 216

JOHNSON CONTROLS
70
FORM 150.62-NM6 (103)
UNIT CONTROLS
YORK MILLENNIUM CONTROL CENTER
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 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, op-
tions, and fault information.
Remote cycling, demand limiting and chilled liquid tem-
perature 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 devia-
tion from setpoint.
A Master ON/Off switch is available to activate or deac-
tivate the unit.
INTRODUCTION MICROPROCESSOR bOARD
The Microprocessor board is the controller and de-
cision 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 con-
stant 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 re-
quirements, and to provide displays.
The on-board power supply converts 24VAC from the 1T
transformer to a +12VDC and +5VDC 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 5VDC supply.
24VAC is rectified and filtered to provide unregulated
+30VDC to supply the flow switch, PWM remote tem
-
perature reset, and demand limit circuitry which is avail-
able to be used with field supplied contacts.
00065VIP
Unit Controls