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Thermostat / Low Voltage Connections
• The furnace is designed to be controlled by a 24 VAC
thermostat. The thermostat's wiring must comply with
the current provisions of the NEC (ANSI/NFPA 70) and
with applicable local codes having jurisdiction.
• The thermostat must be installed according to the
instructions supplied by the thermostat manufacturer.
Low voltage connections (24 VAC) from the thermostat
are wired to the terminal strip on the integrated control in
the furnace.
Figure 28
contains the proper connections
for heating only (two-wire) and heating/cooling (four-
wire) applications. Recommended minimum wire gauge
for thermostat wiring is shown in
• The thermostat should be mounted about 5 feet above
the floor on an inside wall. DO NOT install the thermostat
on an outside wall or any other location where its
operation may be adversely affected by radiant heat from
fireplaces, sunlight, or lighting fixtures, and convective
heat from warm air registers or electrical appliances.
Refer to the thermostat manufacturer's instruction sheet
for detailed mounting information.
• The six pin terminal marked "Expansion Port"
28) is not used in the single stage furnace as shipped
from the factory. It is used for the furnace control board
to communicate to a fixed speed or variable speed high
efficiency motor that may be optionally installed. Please
contact your distributor for the proper upgrade motor
kit.
Heat Anticipator
Set the heat anticipator according to the instructions
supplied by the thermostat manufacturer. To determine
the heat anticipator setting:
1. Add the current draw of the system components; or
2. Measure the current flow on the thermostat R-W circuit
after the circulating blower motor has started.
A/C CONDENSING UNIT
3 AMP
ROOM
FUSE
THERMOSTAT
R
Connect
C
R & W
Y
For Heating
G
Only
W
9
6 3
2
NOTE: The "Y" terminal
8
5
4 1
7
on
the
control
board
must be connected to the
thermostat
for
proper
6 3
cooling mode operation.
2
5
4 1
FIELD WIRING
LOW VOLTAGE
CONNECTION
NEUTRAL LEADS
Figure 28. Low Voltage Field, Four-wire
Heating/Cooling Applications
Table 5 (page
28).
(Figure
CONDENSING UNIT
CONTROL BOX
EXPANSION PORT
(MOTOR CONNECTION)
SPEED
SELECT
STATUS
RED
GREEN
FLAME
YELLOW
180
BLOWER
120
OFF
90
DELAY
60
MOTOR SPEED TAPS
(NOT USED)
ELECTRONIC AIR CLEANER
HUMIDIFIER TAP
Twinning
Single stage furnaces are not supplied with a built-
in twinning capability. Other valuable features and
enhancements were made to the new control that made it
necessary to remove the twinning capability. For twinning
of single stage furnaces with PSC motors, a twinning kit
(920919) is available for purchase. Please follow the
instructions provided with the kit.
If both single stage furnaces are upgraded to the fixed
speed iSEER™ blower, the twin terminal on the blower
control boards
(Figure
29) may be used to twin the single
stage furnaces only if the following criteria are met:
• Both furnaces and motors must be the same size.
• Both motors must be on the same speed for cooling
and heating.
• Both furnaces must have a common return duct and
common supply plenum.
• Both furnaces must be the same phase and on the
same leg of power.
Furnaces equipped with variable speed iSEER™
motors may not be twinned under any circumstances.
For twinning of single stage furnaces equipped with fixed
speed iSEER™ blowers, refer to
and the following instructions:
WARNING:
When servicing either twinned furnace, power
must be turned off on both furnaces. Failure to
comply may result in improper operation leading
to damage to the furnaces or personal injury!
1. Turn off all power to both furnaces.
2. Attach a wire between the two twin terminals on the
twinning control boards. Use field supplied wire and
two 3/16" wire terminals.
NOTE: One furnace can be used for one stage of heating
and the other furnace can be used for the second stage of
heating. The installer also has the choice of running one
furnace only or both furnaces. In both cases the blowers
will run at the same time and at the same speeds:
• Single stage heating: The W connection on each furnace
must be connected together and then connected to
the W connection of the thermostat. This will allow
both furnaces to ignite at the same time for one stage
heating.
• Two stage heating: The W connection on one furnace
must be connected to the W1 connection of the
thermostat. The W connection of the second furnace
must be connected to the W2 connection of the
thermostat. This will allow one furnace to ignite for one
stage of heating and the second furnace to ignite for
the second stage of heating.
3. Refer to
Figure 29
for the remaining thermostat
connections. The C connection must be made between
the twinned furnaces to ensure proper performance.
Figure 29 (page 30)
29
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