JOHNSON CONTROLS
101
FORM 150.73-NM1
ISSUE DATE: 09/04/2020
7
SECTION 7 – UNIT CONTROLS
YORK MILLENNIUM CONTROL CENTER
00065VIP
INTRODUCTION
The YORK MicroComputer Control Center is a mi-
croprocessor 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 suction pressure
or discharge 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
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 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 24 VAC 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 microboard 5 VDC supply.
24 VAC is rectified and filtered to provide unregulated
+30 VDC 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. The Micro-
processor 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.
Summary of Contents for YLUA0078
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