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1.3 UNIT (CHILLER) ON / OFF SWITCH
A master UNIT (Chiller) ON / OFF switch is located
just below the keypad. This switch allows the operator
to turn the entire chiller OFF, if desired. The switch
must be placed in the ON position for the chiller to
operate. Any time the switch is in the OFF position, a
Status message indication will be displayed. See page
103 for the location of this switch.
1.4 MICROPROCESSOR BOARD
The Microprocessor Board(s) controls and makes de-
cisions for the chiller. Information inputs from trans-
ducers and sensors around the chiller are either con-
nected directly to the Microprocessor Board or are con-
nected to the I/O Expansion Board and multiplexed be-
fore being sent to the Microprocessor Board. The Mi-
croprocessor Board circuitry multiplexes all of these
analog inputs, digitizes them, and constantly scans them
to monitor chiller operating conditions. Based on this
information, the Microprocessor issues commands to
the Relay Boards to activate and deactivate contactors,
solenoids, etc. for chilled liquid, operating control, and
safety control.
Commands are sent from the Microprocessor Board to
the I/O Expansion Board to control the slide valves for
chilled liquid control.
Keypad commands are acted upon by the micro to
change setpoints, cutouts, scheduling, operating require-
ments, and to provide displays.
A +12VDC REG supply voltage from the Power Sup-
ply Board is converted to +5V REG by a voltage regu-
lator located on the Microprocessor Board. This volt-
age is used to operate the integrated circuitry on the
board.
System Switches 1 - 4
System Switches for each system are located on the
Microprocessor Board (Section 1.11, Item 5). These
switches allow the operator to selectively turn a given
system on or off as desired.
Internal Clock & Memory Backup Battery
The Microprocessor Board contains a Real Time Clock
integrated circuit chip (Section 1.11, Item 2) with an
internal battery backup. The battery backup assures that
any programmed values (setpoints, clock, cutouts, etc.)
are not lost during a power failure or shutdown period
regardless of the time involved.
YORK INTERNATIONAL
The battery is a 10 year lithium type, but life will depend
upon whether the Real Time Clock's internal clock cir-
cuit is energized. With the clock OFF, a rated life of
approximately 10 years can be expected. With the clock
ON, approximately 5 years. The clock is enabled and
disabled using a jumper on the microprocessor board.
If the chiller is shut down or power failure is expected
for extended periods, it may be desirable to disable the
clock to save battery life. The clock can then be reacti-
vated and reprogrammed when the chiller is returned
to service. This will not affect the maintenance of pro-
grammed values and stored data by the backup battery.
While a chiller is operating, the clock must be ON (Sec-
tion 1.11, Item 1) or the internal clock on the micropro-
cessor will not be active and the micro cannot keep track
of time, although all other functions will operate nor-
mally. Failure to turn the Clock ON could result in the
chiller not starting due to the time "frozen" on the clock
falling outside the Start/Stop time programmed in the
Daily Schedule, see Section 7.3.
1.5 ANCILLARY CIRCUIT BOARDS
Power Supply Board
The on-board switching power supply is fuse protected
and converts 24VAC from the logic transformer 2T to
+12V REG which is supplied to the Microprocessor
Board, Relay Output Boards, and the 40 character dis-
play to operate the integrated circuitry.
24VAC is filtered, but not regulated, to provide unregu-
lated +24VDC to supply the flow switch, PWM remote
temperature reset, PWM remote current reset, lead /
lag select, and remote print circuitry which may be uti-
lized with user supplied contacts.
24VAC is also filtered and regulated to +24VDC to be
used by the optional EMS/BAS Circuit Boards for re-
mote temperature or remote current reset.
Individual rectifier and filtering circuits are present
which receive the Current Transformer signals for each
phase of motor current on each compressor. These cir-
cuits rectify and filter the signals to variable DC. A
phase rotation circuit for each compressor is also present
to assure that the screw compressors do not run in the
wrong direction. All of these signals are sent to the I/O
Expansion Board which multiplexes them and then
feeds them to the Microprocessor Board.
FORM 201.18-NM6
8
99
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