24
YORK INTERNATIONAL
26176A
FIG. 9 – POWER PANEL
A +12V REG supply voltage from the Power Supply Board
is converted to +5V REG by a voltage regulator located
on the Microprocessor Board. This voltage is used to
operate integrated circuitry on the board.
Four system switches located on the Microprocessor
Board activate or deactivate the individual systems (com-
pressors).
POWER SUPPLY BOARD
The on-board switching power supply converts 24VAC
from the 2T transformer to +12V REG which is supplied
to the Microprocessor Board, Relay Board, and 40 Char-
acter Display to operate integrated circuitry.
A rectifier and filtering circuit for each motor current cir-
cuit rectifies and filters these signals to variable DC.
These signals are then fed to the Microprocessor Board.
RELAY OUTPUT BOARD
This board converts 0-12VDC logic level outputs from
the Microprocessor Board to 120VAC levels used by
motor contactors, solenoid valves, etc. to control sys-
tem operation. The common side of all relays on the
Relay Output Board is converted to +12V REG.
The open collector outputs of the Microprocessor Board
energize the DC relays by pulling the other side of the
relay coil to ground. When not energized, both sides of
the relay coils will be at +12VDC potential.
CURRENT TRANSFORMER (C.T.)
A C.T. on the 3
φ
power wiring of each motor sends AC
signals proportional to motor current to the Power Sup-
ply Board which rectifies and filters the signal to variable
DC voltage (analog). This analog level is then fed to the
Microprocessor Board to allow it to monitor motor cur-
rent.
40 CHARACTER DISPLAY
The 40 Character Display (2 lines of 20 characters) is a
liquid crystal display used for displaying system pa-
rameters and operator messages. The display has a
lighted background for night viewing as well as a special
feature which intensifies the display for viewing in direct
sunlight.
KEYPAD
An operator keypad allows complete control of the sys-
tem from a central location. The keypad offers a multi-
tude of commands available to access displays, pro-
gram setpoints, and initiate system commands.
BATTERY BACK-UP
The microprocessor board contains a Real Time Clock
integrated circuit chip with an internal battery back-up.
The purpose of this battery back-up is to assure any
programmed values (setpoints, clock, cut-outs, etc.) are
not lost during a power failure regardless of the time in-
volved in a power outage or shutdown period.
SYS 1 FAN
OVERLOADS
SYS 2 FAN
OVERLOADS
SYS 2 FAN
CONTACTORS
TB1 CONNECTIONS
FOR OPTIONAL
ALARMS,EVAP
PUMP,COND PUMP,
AND L& 2 115 VAC
CONTROL PANEL
SUPPLY
1&2 FUSE
3&4 FUSE
SYS 2 MOTOR
CONTACTORS
SYS 1 MOTOR
CONTACTORS
SYS 1 FAN
CONTACTORS
TB2