York YCAS Series, Installation Operation & Maintenance

Page: 136 / 216

136 YORK INTERNATIONAL
FORM 201.19-NM8 (804)
1.3 UNIT (CHILLER) ON / OFF SWITCH
A master UNIT (Chill er) ON / OFF switch is lo cat ed
just below the keypad. This switch allows the op er a tor
to turn the entire chiller OFF, if desired. The switch must
be placed in the ON po si tion for the chiller to op er ate.
Any time the switch is in the OFF position, a Status
mes sage indication will be displayed. See page 134 for
the location of this switch.
1.4 MICROPROCESSOR BOARD
The Microprocessor Board controls and makes de ci sions
for the chiller. Information inputs from trans duc ers and
sensors around the chiller are either con nect ed di rect ly
to the Microprocessor Board or are con nect ed to the I/O
Expansion Board and multiplexed be fore be ing sent to
the Mi cro proc es sor Board.
The Mi cro pro ces sor Board cir cuit ry multiplexes all of
these analog in puts, dig i tiz es them, and constantly scans
them to mon i tor chill er operating conditions. Based on
this in for ma tion, the Mi cro proc es sor issues commands
to the Re lay Boards to activate and de ac ti vate con tac tors,
so le noids, etc. for chilled liquid, op er at ing control, and
safe ty con trol.
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 re-
quire ments, and to provide displays.
A +12VDC REG supply voltage from the Power Sup ply
Board is converted to +5V REG by a voltage reg u la tor
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 Mi-
croprocessor Board ). These switch es 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
in te grat ed circuit chip (Section 1.11, Item 2) with an
in ter nal battery backup. The battery backup assures that
any programmed values (setpoints, clock, cutouts, etc.)
are not lost during a power failure or shutdown period
re gard less of the time involved.
The battery is a 10 year lithium type, but life will de-
pend upon whether the Real Time Clock’s internal clock
cir cuit is energized. With the clock OFF, a rated life of
ap prox i mate ly 10 years can be expected. With the clock
ON, approximately 5 years. The clock is enabled and
dis abled 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 re ac ti vat ed and
reprogrammed when the chiller is returned to ser vice.
This will not affect the maintenance of pro grammed
values and stored data by the backup bat tery.
While a chiller is operating, the clock must be ON (Sec-
tion 1.11, Item 1) or the internal clock on the mi cro pro -
ces sor will not be active and the micro cannot keep
track of time, although all other functions will operate
nor mal ly. 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 Sup ply 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 Out put Boards, and the 40 character dis-
play to operate the in te grat ed circuitry.
24VAC is fi ltered, but not regulated, to provide un reg u-
lat ed +24VDC to supply the fl ow switch, PWM re mote
tem per a ture reset, PWM remote current reset, lead / lag
select, and remote print circuitry which may be uti lized
with user supplied contacts.
24VAC is also fi ltered and regulated to +24VDC to be
used by the optional EMS/BAS Circuit Boards for re-
mote tem per a ture or remote current reset.
Individual rectifi er and fi ltering circuits are present
which re ceive the Current Transformer signals for each
phase of motor cur rent on each compressor. These
cir cuits rec ti fy and fi l ter the signals to variable DC. A
phase ro ta tion circuit for each compressor is also pres-
ent to as sure that the screw compressors do not run in
the wrong di rec tion. All of these signals are sent to the
I/O Ex pan sion Board which multiplexes them and then
feeds them to the Microprocessor Board.
Micro Panel Contents