268894-UIM-A-0407
Unitary Products Group
13
Single-Wire Twinning
The control in the furnace has the single-wire twinning feature. With this
feature, a single wire is connected between the TWIN terminal on one
furnace board to the TWIN terminal on the second furnace board. The
board then communicates the blower status from one furnace to the
other along this wire. This communication makes the second furnace
blower come on at the same time, and on the same speed, as the first
furnace blower.
Single-Wire Twinning Instructions
Connect the control wiring as shown in Figure 12.
1.
Connect the low voltage wiring from the wall thermostat to the ter-
minal strip on the control board of Furnace #1.
2.
Connect a wire from the TWIN terminal of Furnace #1 to the TWIN
terminal of Furnace #2.
3.
Install a separate 24V relay as shown in the diagram below. Use of
this relay is required, as it ensures that the transformers of the two
furnaces are isolated, thus preventing the possibility of any safety
devices being bypassed.
Single-Wire Twinning Operation
Heating - On a call for heat (W signal) from the wall thermostat, both
furnaces will start the ignition sequence and the burners on both fur-
naces will light. About thirty seconds after the burners light, the blowers
on both furnaces will come on in heating speed. When the thermostat is
satisfied, the burners will all shut off and, after the selected blower off
delay time, both blowers will shut off at the same time. The twinning
control ensures that both blowers come on and shut off at the same
time.
Cooling - On a call for cooling (Y signal) from the wall thermostat, both
furnace blowers will come on at the same time in cooling speed. When
the thermostat is satisfied, both blowers will stay on for 60 seconds,
then will shut off at the same time.
Continuous Fan - On a thermostat call for continuous fan (G signal),
both furnace blowers will come on at the same time in cooling speed
and will stay on until the G signal is removed.
STAGING
In applications where more heating capacity or more airflow capacity is
needed than what one furnace can deliver, twinning can be used to
make two furnaces operate in tandem, using one duct system and one
room thermostat. This control can also be used along with a two-stage
wall thermostat to stage two twinned furnaces, making them operate
like a single two-stage furnace. This allows only one furnace to supply
heat during times when the heat output from one furnace is sufficient to
satisfy the demand. When one duct system is used for two furnaces, it
is necessary that the two blowers operate in unison. The twinning func-
tion of this board ensures that both blowers turn on and off simulta-
neously, and operate on the same blower speed. Even when only one
furnace is supplying heat, both furnace blowers must run.
Single-Wire Staging
The single-wire twinning feature of this board can also be used for stag-
ing of two furnaces. With this feature, a single wire is connected
between the TWIN terminal on one furnace board to the TWIN terminal
on the second furnace board. The board then communicates the blower
status from one furnace to the other along this wire. This communica-
tion makes the second furnace blower come on at the same time, and
on the same speed, as the first furnace blower.
Single-Wire Staging Instructions
Connect the control wiring as shown in Figure 13.
1.
Connect the low voltage wiring from the wall thermostat to the ter-
minal strip on the control board of Furnace #1. For staging applica-
tions, the wire from thermostat W1 is connected to the W
connection on the board on Furnace #1. The wire from thermostat
W2 is connected to Furnace #2 through a separate relay, as
described below.
2.
Connect a wire from the TWIN terminal of Furnace #1 to the TWIN
terminal of Furnace #2.
3.
Install a separate 24V relay as shown in the diagram below. Use of
this relay is required, as it ensures that the transformers of the two
furnaces are isolated, thus preventing the possibility of any safety
devices being bypassed.
Single-Wire Staging Operation
Heating - On a call for first-stage heat (W1 signal) from the wall thermo-
stat, Furnace #1 will start the ignition sequence and the burners will
light. About thirty seconds after the burners light, the blowers on both
furnaces will come on in heating speed. When the thermostat is satis-
fied, the burners will shut off and, after the selected blower off delay
time, both blowers will shut off at the same time. On a call for second
stage of heat, the burners of Furnace #2 will also light and both blowers
will run. The twinning control ensures that both blowers come on and
shut off at the same time.
Cooling - On a call for cooling (Y signal) from the wall thermostat, both
furnace blowers will come on at the same time. When the thermostat is
satisfied, both blowers will stay on for 60 seconds, then will shut off at
the same time.
Continuous Fan - On a thermostat call for continuous fan (G signal),
both furnace blowers will come on at the same time in cooling speed
and will stay on until the G signal is removed.
FIGURE 12:
Single Stage Twinning Wiring Diagram
W
G
C
R
Y
TWIN
TO A/C
WALL THERMOSTAT
W
G
R
Y
ISOLATION
RELAY
FURNACE 2 CONTROL BOARD
W
G
C
R
Y
TWIN
FURNACE 1 CONTROL BOARD
FIGURE 13:
Two-Stage Twinning Wiring Diagram
W
G
C
R
Y
TWIN
TO A/C
WALL THERMOSTAT
W1
G
R
Y
ISOLATION
RELAY
FURNACE 2 CONTROL BOARD
W
G
C
R
Y
TWIN
FURNACE 1 CONTROL BOARD
W2
