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wires out of the top hole in each
control box and through the
strain relief bushing.
a. The blue wires connect the
original door switch 1, through
the new door switch in
furnace 2, and to terminal "L 1"
of control board 1.
b. Similarly, the yellow wires
connect the original door
switch 2, through the new
door switch in furnace 1 and
to terminal "L 1" of control
board 2.
c. The red wire connects the two
electronic air cleaner (EAC)
screw terminals on both
control boards.
d. Secure the line voltage wires
with strain relief bushings at
the 7/8" dia. hole where they
exit the control boxes.
8. Connect control power (24 VAC)
from terminal board "R" in
furnace 1 to the "24VAC"
terminal (1/4" push on) on the
control board in furnace 2. Use
the 4" piggyback terminated red
wire and wire nut connector.
9. Connect control (24VAC) wires
between thermostat terminals
"W', "Y", "G" and "C" on furnace
control boards 1 and 2.
10. Install a control thermostat (field
supplied) according to its
instructions to FURNACE 2.
IMPORTANT: ELECTRICAL
POWER TO BOTH FURNACES
MUST BE SHUT OFF WHEN
WIRING THE THERMOSTAT. THE
FURNACE CONTROL SYSTEM
TERMINAL "C" (COMMON) IS
CONNECTED TO THE (CABINET)
GROUND AS PART OF THE FLAME
SENSE CIRCUIT. ACCIDENTAL
SHORTING OF THERMOSTAT
WIRES TO GROUND DURING
INSTALLATION CAN DAMAGE THE
CONTROL TRANSFORMER.
11. Control voltage power (24
VAC) to the thermostat must
be supplied from thermostat
terminal "R" on the control
board in furnace 2. Connect the
thermostat to "W" (heat), "Y"
(cool), and "G" (fan) that are now
common to both furnaces as
shown in the wiring diagram.
Connect the remote compressor
contactor (CC) leads to terminals
"Y" (cool) and "C" (common) that
also are common to both
furnaces.
If the thermostat has an
adjustable heating anticipator,
set it for approximately 0.8 amps
or the measured current
amperage. Do this after the
furnaces are in operation.
12. Use the provided wire ties to
secure the interconnecting and
thermostat wiring in place to
avoid contact with exposed
edges, moving parts, or service
procedures. Field provide
additional materials, if required.
Attach the wiring diagram from
the kit to one furnace.
13. Replace the blower compartment
doors and check that the doors
fit correctly. Adjust the fit if
required to assure easy removal
and installation by the user when
servicing air filters.
14. Complete the furnace installation
and put the furnaces in operation
following the furnace installation
and operating instructions.
Make all proper operational and
safety checks. Remove the blower
compartment doors individually and
ensure that electrical power to both
furnaces is shut off when either door
is off.
NOTE: This twinning kit cannot be
used for heat pump fossil fuel kit
applications.
NOTE: Two parallel condensing units
may be used for twinning applications
by wiring the control circuits (4) in
parallel.
OPERATION
The furnaces operate essentially the
same as they would if installed
individually except that the indoor air
blowers operate simultaneously. This
is essential when the furnaces are
connected to a common duct system.
Each furnace may vary the start of its
burner operation by a few seconds.
Both furnaces start its induced draft
blower when the thermostat calls for
heat. But each furnace starts its
prepurge and trial for ignition only
after its pressure switch closes.
A delay between burner firings may
occur dependant on individual
pressure switch calibration, induced
draft blower operation, furnace
components, and combustion air inlet
or vent pipe configuration. Both
indoor air blowers should start
approximately 20 seconds after the
first burner lights and continue
operation.
At the end of a heat call, both burners
and induced draft blowers shut down.
Both indoor air blowers continue to
run until the control board with the
longest off time delay setting is
satisfied. Both furnace control boards
should be set for the same blower off
delay time.
Each furnace ignition control
supervises its own burner operation.
It is possible for one furnace to lock
out due to ignition failure or failure to
sense flame. The other furnace could
continue to operate and satisfy the
thermostat. The locked out control
would reset during the off cycle and
could operate normally during the
next call for heat. If one furnace
becomes disabled, the second
furnace continues to operate .
If a high limit control opens on either
furnace, both gas controls close and
both indoor air blowers continue to
operate. The induced draft blower
remains on in the furnace with the
open limit, and the induced draft
blower shuts off in the other furnace.
If the limit resets and the thermostat
continues to call for heat, the furnace
immediately initiates an operating
cycle. Both indoor blowers continue
to operate through the blower off
delay time, then stop. The furnace
that had the open limit initiates an
operating cycle. Both indoor air
blowers restart approximately 20
seconds after the first burner lights.
Burner ignition of the furnace that had
an open limit could be delayed up to
four minutes after the first burner
lights.
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