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TABLE 9
FIELD WIRE SIZE FOR 24 VOLT CONTROL CIRCUITS
3.0
2.5
2.0
Wire length equals twice the run distance
NOTE: Do not use 24 volt control wiring smaller than No. 18.
FIGURE 42
ISOLATION RELAY
FURNACE TWINNING
INSTALLATIONS
NOTE: Run furnaces as individual
furnaces before trying to twin or when
troubleshooting.
Twinning operation of two furnaces,
installed side-by-side, connected by a
common duct system with main power
supplied by the same source, and
controlled by a common thermostat can
be done with the UT Electronic Controls
1095-204 integrated control boards.
Only twin identical furnaces with
identical control boards.
Furnaces must have same heating
and blower capacity.
Ž
Only bottom returns can be used.
(Upflow models only)
No more than two furnaces (a pair)
can share the same supply and
return.
NOTE: Duct system must be adequate
to provide correct airflow to each
furnace for supply and return.
IMPORTANT: Twinning furnaces must
operate off the same phase of power.
44
SOLID COPPER WIRE - AWG
16
14
12
16
14
12
18
16
14
50
100
150
LENGTH OF RUN - FEET
It should be noted that both blowers will
run simultaneously when there is a call
for heating, cooling or fan.
The status LED will display blink code 5
if twinning is not set up properly (refer to
Troubleshooting diagram in the back of
this manual).
IMPORTANT: Only two furnaces on a
single thermostat.
UT ELECTRONIC CONTROLS
1095-201 or 204
TWO-STAGE TWINNING OPERATION
USING A SINGLE-STAGE
THERMOSTAT
A two-stage thermostat will give the
most optimum performance. The
furnace (when twinned) can operate
using a single-stage thermostat.
OPTION A: To run both units together
as a single-stage furnace with NO
staging (100% high heat always) wire
the two furnaces together as shown in
Figure 43.
Both controls must have jumper P6 in
the "TWIN" position (see Figure 48).
Both controls must have jumper P7 in
the "5" or "7" position (see Figure 48).
OPTION B: Both controls must have
jumper P6 in the "TWIN" position (see
ST-A0804-01
Figure 48).
Both controls must have jumper P7 in
the "5" or "7" position (see Figure 48).
For the first fire or twelve minutes of
operation, the furnace will run at low
fire. If the thermostat does not satisfy
in fire or twelve minutes, the furnaces
will automatically switch to high fire
and will run on high fire until the
thermostat is satisfied. See Figure 43
for the wiring diagram for this
configuration.
TWO-STAGE OPERATION
(See Figure 45)
a. Control board "ONE" is on
furnace connected to the
thermostat.
b. The 24 VAC supply to both
control boards must be in
phase with each other.
c. Connect the "C," "W1," "W2,"
"Y," and "TWIN" terminals to
counterparts on each control.
d. Both control boards must have
jumper P6 in the "TWIN"
position (see Figure 48).
Both controls must have
jumper P7 in the "NONE"
position (see Figure 48).
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