16
YORK INTERNATIONAL
SINGLE CIRCUIT UNITS
INTRODUCTION
The YORK MicroComputer Control Panel is a micropro-
cessor based control system. The microprocessor con-
trols the unit as needed to maintain chilled water tem-
perature.
A 4-digit display (See Fig. 5 or 6) allows the operator to
select 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)
• % Full Load Motor Current
• Suction Pressure PSIG (kPaG x 10)
• Oil Pressure, PSID (kPaD x 10)
• Discharge Pressure PSIG (kPaG x 10)
• Suction Pressure Cutout Setting, PSIG (kPaG x 10)
The system “Return Chilled Water Temp” is entered by
two rotary switches and the “Water Cooling Range” by a
single rotary switch.
The system can be activated by a toggle switch. The
switch normally remains “ON” after start-up.
Remote cycling and Return Chilled Water Temp Set-
point Reset can be accomplished as noted on Page 23.
Loading and unloading decision making is done by soft-
ware on the Micro Logic Board. These decisions are
made according to temperature deviations from the se-
lected setpoint and the selected cooling range resulting
in more precise control of water temperature.
SYSTEM DESCRIPTION
MICROLOGIC 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
Boards and provides system control through the Relay
Output Board.
DIGITAL INPUT BOARD (Optional)
This board allows use of optional remote 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 comparison to safety thresholds.
The on-board power supply converts AC input from trans-
former 2T to DC voltages of +5V UNREG, +5V REG,
+12V UNREG, +12V REG, and –12V UNREG for sup-
ply 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 the compressor.
*Metric values require the EPROM and Control Panel to be changed.
This option can be ordered through Product Marketing.
