7. Dress wires to ensure they do not contact sharp or moving parts nor interfere with blower operation, removal of filters, or operation of
switches.
8. Make all thermostat connections to LH furnace only.
Two-Stage Heat with 2-Stage Gas-Heat Thermostat (Field Supplied)
NOTE:
ALL thermostat connections are to be made to LH furnace control ONLY. (See Fig. 15.)
NOTE:
This application allows both furnaces to operate in low heat for first-stage heat mode or both furnaces to operate in high heat for
second-stage heat mode as determined by a 2-stage thermostat. See furnace Installation, Start-Up, and Operating Instructions for further details
on this heating mode.
To operate furnaces in 2-stage heating mode when a 2-stage thermostat controls the staging, install twinning kit as described in the two-stage heat
with single-stage gas heat thermostat:
a. Turn LHT set-up switch on L/H control board to “ON.”
b. Turn LHT set-up switch on R/H control board to “ON.”
NOTE:
ALL other 2-stage thermostat connections are to be made to LH furnace control ONLY. (See Fig. 15.)
PROCEDURE 3—CONNECT ELECTRICAL COMPONENTS-COOLING
WARNING: FIRE HAZARD
Failure to follw warning could result in fire, personal injury or death.
Make no connections between the R 24-vac connector in 1 furnace and the R 24-vac connector in other furnace. Failure to follow this
warning can cause a fire, personal injury, or death.
When installing twinned outdoor units with twinned gas furnaces, it is necessary to use a field-supplied 24-vac pilot-duty relay and a field-supplied
24/115-vac transformer as shown in Fig. 13, 14, or 15 to prevent overloading furnace 24/115-vac transformer.
PROCEDURE 4—VENTING
Refer to Installation, Start-Up, and Operating Instructions supplied with each furnace for venting information.
CAUTION: When common-venting twinned, Category I (negative-pressure venting), non-condensing furnaces, exces-
sive condensate may occur as a result of oversized vent systems. Dedicated vents and/or proper vent sizing, per the current
edition of the National Fuel Gas Code, will reduce the potential for condensation.
PROCEDURE 5—GAS SUPPLY PIPING
NOTE:
All gas connections must be made through exposed outer side of each furnace. Do not common connect any connection other than supply-
and return-air ducts.
Furnaces are recommended to be provided with a single shutoff valve. However, individual shutoff valves may be required by local codes or
jurisdictions. Refer to Installation, Start-Up, and Operating Instructions provided with each furnace for additional gas supply information.
PROCEDURE 6—ELECTRICAL SUPPLY CONNECTIONS
NOTE:
All electrical power connections must be made through exposed outer side of each furnace. Do not common connect any connection other
than supply- and return-air ducts.
1. Each furnace shall be connected to its own 115-vac power supply. The twinning kit installation interconnects the furnaces, allowing them
to operate as a single furnace. The L1 (black) connection to each furnace must be connected to circuit breakers connected to the same service
panel 115-vac phase leg.
On single-phase (residential) systems, each furnace circuit breaker should be located directly across from each other in service panel, or each
furnace circuit breaker should be located on the same side of service panel, but must skip 1 space to be connected to the same leg of the
1-phase power supply.
On 3-phase (commercial) systems, each furnace circuit breaker should be located directly across from each other in service panel, or each
furnace circuit breaker should be located on the same side of service panel, but must skip 2 spaces to be connected to the same leg of the
3-phase power supply.
The proper 115-vac phasing of furnace connections permits 24-vac transformer phasing as described below.
2. Phasing of the connected 24-vac transformer secondary circuits can be determined with the LED status of both furnaces. See furnace
Installation, Start-Up, and Operating Instructions and status code labels on blower doors. The furnaces’ transformers’ black leads should
be connected to PR1 connectors and white leads to PR2 connectors on controls. If 1 or both LEDs are rapidly flashing, disconnect lead at
TEST/TWIN terminal of LH furnace and observe LED at each furnace.
To verify that the furnaces are in phase, check from Main furnace L1 to Secondary furnace L1 with a voltmeter. If the furnaces are in phase,
the voltage between both furnaces will be ZERO.
Fig. 12—LHT Switch Settings
A02221
LHT
OFF
DLY
OFF
ON
1 2 3
Thermostat Type
Left Hand
Right Hand
LHT Switch 1
LHT Switch 1
Single Stage
Thermostat
OFF
ON
Two Stage
Thermostat
ON
ON
—17—
