39
FURNACE TWINNING
INSTALLATIONS
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 1028-928
integrated control boards.
IMPORTANT: Twinning of 90RJ and
90TJ units requires an accessory
twinning kit. Refer to the specification
sheet for proper kit. Do not attempt to
twin these models by using the
instructions below.
IMPORTANT: Only twin furnaces
with identical control boards.
IMPORTANT: Only bottom returns
can be used. No more than two
furnaces can share the same supply
and return. Furnaces must have
same heating and blower capacity.
Twinning furnaces must operate off
the same phase of power.
It should be noted that both blowers
will run simultaneously when there is
a call for heating, cooling or fan.
The “OK” LED will flash if twinning is
not set up properly.
UT ELECTRONIC CONTROLS
1028-928 CONTROL BOARD
1. Single Stage Operation
(See Figure 41)
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,” “W” and
“TWIN” terminals to
counterparts on each control.
d. Both control boards must have
switch #3 in the “ON” position.
2. Two Stage Operation
(See Figure 42)
a. Follow above instructions.
Connect “W2” on thermostat
to “W” on control board
“TWO.”
fireplace, sun rays, lamps, televisions,
radios or air streams from registers.
Refer to instructions packed with the
thermostat for “heater” selection or
adjustment.
ACCESSORIES
FIELD-INSTALLED
OPTION ACCESSORIES
ELECTRONIC AIR CLEANER
Line voltage power can be supplied
from the screw terminal “EAC” and a
line voltage neutral screw terminal on
the control board. NOTE: Spade
terminals only are provided on 90RJ
and 90TJ models. This will power the
electronic air cleaner whenever the
circulating air blower is in operation.
HUMIDIFIER
Line voltage power can be supplied
from screw terminal “HUM” to a line
voltage neutral screw terminal on the
control board. This will power the
humidifier whenever the burner is
on and the circulating air blower is
operating in the heating mode.
NOTE: Maximum current – 1.0 amps
for each option.
NOTE: Humidifier output is not
available on 90RJ and 90TJ models.
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