York YLUA0248 Series, Installation Operation & Maintenance

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JOHNSON CONTROLS
95
FORM 150.73-NM2
ISSUE DATE: 09/07/2020
7
SECTION 7 – UNIT CONTROLS
YORK
MILLENNIUM
CONTROL CENTER
00065VIP
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 log-
ic embedded in the microprocessor based control sys-
tem will provide control for the suction pressure or dis-
charge air temperature, 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 program-
ming 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 sup-
plied contacts.
Compressor starting/stopping and loading/unload-
ing decisions are performed by the Microprocessor to
maintain suction pressure or discharge air temperature.
These decisions are a function of temperature or pres-
sure deviation from setpoint.
A Master ON/Off switch is available to activate or de-
activate the unit.
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
connected directly to the Microprocessor Board. The
Microprocessor Board circuitry multiplexes the ana-
log inputs, digitizes them, and scans them to keep a
constant watch on the unit operating conditions. From
this information, the Microprocessor then issues com-
mands to the Relay Outputs to control contactors, sole-
noids, 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 volt-
age 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 unregulat-
ed +30VDC 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 120VAC to motor contactors, solenoid valves,
etc. to control system operation. 120VAC is supplied
to the optimal T3 Transformer, which supplies 12VAC
to the bridge diode module. The Bridge Diode Module
rectifies the voltage to -12V unreg. The +12V unreg
voltage supplies power to the Remote Temp. Reset Cir-
cuit Board.