98
FORM 160.54-M1
ISSUE DATE: 10/25/2019
SECTION 6 - I/O BOARD
JCI COMPANY CONFIDENTIAL
JOHNSON CONTROLS
TRIACS
Triacs are used to control the Pre-rotation Vanes ac-
tuator, Refrigerant Level Variable Orifice actuator and
Variable Geometry Diffuser actuator (certain compres-
sors only) (Refer
,
).
An actuator has an open winding and a close winding.
Current flowing through a winding will cause the ac-
tuator shaft to rotate in the respective direction. Each
winding is controlled by a Triac.
When a Triac is turned ON, it permits current to flow
through the actuator winding, causing the actuator
shaft to rotate. Under Program control, the microboard
turns the Triacs ON and OFF by applying control sig-
nals to the respective Triac Driver. The Triac Driver
is an optocoupler device that isolates the microboard
low voltage circuits from the higher actuator voltages.
To turn on the Triac, the microboard drives the Triac
Driver input to logic low (less than +1 VDC) level. The
Triac driver responds 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 +12 VDC. The Triac Driver responds by
opening the short from triac Gate to Triac terminal 2.
A voltmeter can be used to determine if a Triac is turned
ON or OFF. Measure across the Triac; from Triac ter-
minal 1 to Triac terminal 2. When the Triac is turned
OFF, the voltage will be approximately 20 to 30 VAC;
when turned ON, it will be less than 10 VAC.
The Pre-rotation Vanes Actuator and Variable Geome-
try Diffuser actuator are manufactured by Barber-Cole-
man. This actuator has three windings; a Field wind-
ing and two direction windings. One direction winding
produces clockwise rotation, the other produces coun-
terclockwise rotation. The 115 VAC applied to the
Field Winding induces a 20 to 30 VAC voltage into
each of the direction windings. The desired rotation is
produced by shorting the Actuator common terminal to
the appropriate direction terminal, causing current to
flow in the direction winding. As described previously
in this section, Triacs control the current through the
open and close windings.
The Refrigerant Level Variable Orifice Actuator on
new production chillers is manufactured by Belimo.
This actuator has two windings; open and close. One
winding produces clockwise rotation and one produces
counterclockwise rotation. This actuator operates from
24 VAC. As described previously in this section, Triacs
are turned ON to allow current to flow through the ap-
propriate winding to produce the desired rotation. If
the OptiView Control Center is retrofit to an existing
chiller, it could be equipped with a Barber-Coleman
Level Actuator that operates as described above.
Chillers equipped with the Variable Geometry Diffuser
are supplied with and require I/O Board 031-01743-
002. This board is populated with the required Triacs
Q3 and Q4 that apply the open and close signals to the
Variable Geometry Diffuser ring actuator. See
TION 26 - VARIABLE GEOMETRY DIFFUSER.
RELAY TIMING
Under Program control, the relays are energized and
de-energized producing contact operation as follows.
Unless otherwise noted, contact rating is 5 amps resis-
tive or 2 Amps inductive at 250 VAC.
K0 - Chilled Water Pump Starter (TB2-44/45)
Dry closure contacts are used. When the chiller is start-
ed, the Contacts close 13 seconds after the start of Sys-
tem Pre-lube. Normally, they open coincident with the
completion of System Coastdown with the following
exceptions:
A. If a LEAVING CHILLED LIQUID - LOW TEM-
PERATURE cycling shutdown occurs, they do
not open at the completion of System Coastdown.
They remain closed for the duration of the shut-
down or until the keypad COMPRESSOR switch
is placed in the Stop-Reset (O) position, where-
upon they open.
B. If Microboard Program Switch SW1-8 is in the ON
position, they do not open at the completion of Sys-
tem Coastdown when the chiller shuts down on a
MULTIUNIT CYCLING - CONTACTS OPEN
or SYSTEM CYCLING - CONTACTS OPEN cy-
cling shutdown. They remain closed for the duration
of the shutdown or until the keypad COMPRES-
SOR switch is placed in the Stop-Reset (O) position,
whereupon they open.
C. With software version C.OPT.01.23.307 (and lat-
er), while “Leaving Chilled Liquid – Flow Switch
Open” cycling shutdown is active, the contacts re-
main closed until the chiller is given a stop com-
mand or has another fault.