48
YORK INTERNATIONAL
DUAL CIRCUIT UNITS
INTRODUCTION
The YORK MicroComputer Control Panel is a micropro-
cessor based control system. The microprocessor con-
trols a 2 system (dual circuited) unit as needed to main-
tain chilled water temperature.
A 4-digit display (see Fig. 30) allows the operator to se-
lect and display system operating parameters via two
“Select Data Display” rotary switches. ENGLISH or
METRIC (optional*) values can be displayed. These
parameters are:
• Return Chilled Water Temperature °F (°C)
• Leaving Chilled Water Temperature °F (°C)
• Low Leaving Water Cutout Temperature °F (°C)
• Return Chilled Water Setpoint °F (°C)
• System 1 % Full Load Motor Current
• System 1 Suction Pressure, PSIG (kPaG x 10)
• System 1 Oil Pressure, PSID (kPaD x 10)
• System 1 Discharge Pressure, PSIG (kPaG x 10)
• System 2 % Full Load Motor Current
• System 2 Suction Pressure, PSIG (kPaG x 10)
• System 2 Oil Pressure, PSID (kPaD x 10)
• System 2 Discharge Pressure, PSIG (kPaG x 10)
• Suction Pressure Cutout Setting, PSIG (kPaG x 10)
(Also see Page 50 for a complete list.)
The system “Return Chilled Water Temp” is entered by
two rotary switches and the “Water Cooling Range” by a
single rotary switch.
System 1 and 2 can be activated by 2 toggle switches.
These switches normally remain “ON” after start-up. A
toggle switch is available to select compressor #1 as
the lead or lag system.
Remote cycling, unloading, and Return Chilled Water
Temp. Setpoint Reset can be accomplished as noted
on Pages 55 & 56. Loading and unloading decision
making is done by software on the Micro Logic Board.
These decisions are made according to temperature
deviations from the selected setpoint and the selected
cooling range resulting in more precise control of water
temperature.
SYSTEM DESCRIPTION
MICRO LOGIC BOARD
The Micro Logic Board is the controller and “decision
maker” in the control panel. It looks at system inputs via
the R. P. Relay, Combo Board, and optional Digital Input
*Metric values require the EPROM and Control Panel to be changed.
This option can be ordered through Product Marketing.
Board and provides system control through the Relay
Output Board.
DIGITAL INPUT BOARD (Optional)
This board allows use of optional remote unloading, re-
mote cycling and remote chilled water temp. select.
These remote inputs are converted to logic levels for
use by the Micro Logic Board.
COMBO BOARD
This board receives analog information from transducer
(pressure) and thermistor (temperature) inputs and
routes the data to the Micro Logic Board where it is used
to control the system. These inputs are serially trans-
mitted to the micro board through the use of a multi-
plexer. On the micro board these analog signals are
converted to digital data to provide displays, to control
system operation, and for comparison to safety thresh-
olds.
The on-board power supply converts an AC input from
transformer 2T to DC voltages of +5V UNREG, +5V
REG, +12V UNREG, +12V REG, and –12V UNREG
for supply voltages to operate the integrated circuitry in
the panel.
MOTOR CURRENT BOARD and CURRENT
TRANSFORMERS (C.T.’s)
C.T.’s on the 3
f
power wiring of each motor send AC
signals proportional to motor current to the Combo Board
which rectifies and filters the signal to variable DC volt-
age (analog). This analog level is then fed to the Micro
Logic Board to allow it to monitor motor current.
RELAY OUTPUT BOARD
This board converts logic level outputs from the Micro
Logic Board to 120VAC levels used by motor contactors,
solenoids, etc. which allows the Micro Logic Board to
control the system operation. The common side of all
relays on the Relay Board is connected to +12VDC un-
regulated. The open collector outputs of the micro board
energize or de-energize DC relays by pulling the other
side of relay coil to ground. When not energized, both
sides of the Relay Coil will be at +12VDC unregulated
potential.
R. P. RELAY (Run Permissive)
The R. P. Relay allows connection of remote start/stop
and flow switch contacts to the system. Opening the cir-
cuit stops both compressors.
