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The I/O (input/output) Board conditions the Digital In-
puts for the Microboard and conditions the Microboard's
Digital Outputs for application to other com po nents and
devices. The left side of the I/O Board per forms the Digi-
tal Inputs function; the right side per forms the Digital
Outputs function. Refer to Fig. 13.
Dig i tal Inputs are on/off inputs to the Microboard from
relay and switch con tacts, such as fl ow switch es, start/
stop switch, and remote cycling/safe ty devices (ref. Fig.
14). The Micro reads the state of these contacts and re-
acts per the Program in struc tions. The contact volt age is
115 VAC when closed and 0VAC when open. These volt-
ages are not suitable for direct input to the Microboard.
There fore, the I/O Board converts the 115VAC/0VAC
contact voltages to 0VDC/+5VDC log ic lev el inputs for
the Microboard. Individual Opto-cou pler cir cuits (ref.
Fig. 15) perform the conversion for each Dig i tal In put.
When the input is 115VAC, the out put will be 0VDC;
when the input is 0VAC, the output will be +5VDC.
Field connected Digital Inputs, such as those from ex-
ter nal devices that cycle the chiller, are connected to
ter mi nal strip TB4 (ref. Fig.14). These inputs are in the
form of dry contacts connected as shown in Fig. 16. The
115VAC power source that is switched by the re mote
contacts is supplied by the I/O Board TB4-1. There are
multiple TB4-1 terminals located adjacent to the fi eld
in put connections, as shown in Fig. 13 and 14.
Digital Outputs are on/off outputs from the Microboard
that control solenoid valves, motor contactors, ac tu a tors,
system relays and provide operating status to ex ter nal
devices (ref. Fig. 17). Per Program in struc tions, the
Microboard energizes and de-energizes these de vic es.
The coils of these devices operate on 115VAC and there-
fore cannot be directly connected to the Microboard.
The Digital Outputs section of the I/O Board contains
+12VDC coil relays that are driven by the Microboard's
logic level outputs. The contacts of these +12VDC relays
operate the external 115VAC coil de vic es. On the I/O
Board, one side of the each of the relay coils is perma-
nently connected to +12VDC at J19-26/27. The other
side of each relay coil is connected to the Microboard
via I/O Board con nec tor J19. The Microboard energizes
each relay by driving the ap pro pri ate input at J19 to logic
low volt age level (ground potential). The DC voltage
at the ap pro pri ate input pin at J19 will be a logic high
(>+10VDC) when the Microboard is com mand ing a
relay to de-en er gize; logic low (<+1VDC) when com-
manding a relay to energize.
YORK INTERNATIONAL
SECTION 4
I/O BOARD
(REFER TO FIG. 13 - 17)
Relay K18 is different from all other relays on the I/O
Board; it has a 115VAC coil. It provides the start/stop
signal to the Compressor Motor Starter and provides
Compressor Run status to remote devices (ref.
Fig.17). Re lay K18 is controlled by DC relays K13
(start) and K14 (stop). To start the compressor motor,
the Microboard en er giz es K13 and K14 simultane-
ously. The 115VAC at TB1-6 is applied to the coil of
K18 via K13 con tacts, en er giz ing K18. Ap prox i mate ly
0.2 seconds later, K13 is de-en er gized. K18 remains
energized through K14 con tacts and holding contacts
of K18. To stop the com pres sor motor, the Microboard
de-en er giz es K14. To prevent sags in Utility Power from
chat ter ing K18, the holding contact of K18, along with
the contact of K13, creates an anti-chatter circuit for
relay K18. Once en er gized, K18 can not be re-energized
un til K13 is again energized; this will not occur until
after a controlled shut down has oc curred and another
start se quence has been initiated.
There are conditions external to the I/O Board required
to energize relay K18. The 115VAC will be present at
TB1-16 only if the motor controller contacts "CM" are
closed and the circuit between external Terminal Strip
TB6-1 and TB6-53 is closed. The "CM" are located on
the CM-2 Board (relay K1), Electro-Mechanical start er
applications, the Solid State Starter Logic Board (relay
K1), Solid State Starter applications or a relay mount ed
on the Variable Speed Drive Logic Board on Variable
Speed Drive applications. The High Pressure safety
switch "HP", must be closed and the RUN Switch
"1SS" must be in the RUN position.
Triacs are used to control the Pre-Rotation Vanes
Ac tu a tor and the Refrigerant Level Variable Orifi ce
Ac tu a tor (ref. Fig. 17 & 49). An actuator has an open
wind ing and a close winding. Current fl owing through
a wind ing will cause the actuator shaft to rotate in the
re spec tive di rec tion. Each winding is controlled by a
Triac. When a Triac is turned on, it permits current to
fl ow through the actuator winding, causing the ac tu a tor
shaft to ro tate. Under Program control, the Microboard
turns the Triacs on and off by applying control signals
to the re spec tive Triac Driver. The Triac Driv er is an
optocoupler device that isolates the Microboard low
voltage cir cuits from the higher actuator voltages. To
turn on the Triac, the Microboard drives the Triac Driv er
input to logic low (<+1VDC) level. The Triac driv er
re sponds by shorting the Triac GATE to Triac terminal
2. To turn the Triac off, the Microboard opens its input
to the Triac Driver and allows the input to pull up to
+12VDC. The Triac Driver responds by opening the
FORM 160.54-M1(503)
4
37
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