4. Two-Stage Heating using Fixed Capacity Furnaces with Two-Stage Gas-Heat Thermostat (Field Supplied) (See Fig. 14.)
NOTE: This modification allows LH furnace only to operate in heating mode for first-stage heat or both furnaces to operate in heating mode for
second-stage heat 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 above, then modify
TKR wiring as follows:
CAUTION: UNIT DAMAGE HAZARD
Failure to follow this caution could result in intermitted furnace operation and unit damage.
Supply-air temperature will be uneven left-to-right when only main system is operating.
Fig. 29—Twinning Kit Installed on Single-Speed and 2-Stage Condensing Furnaces
(AFTER Serial No. 2894A00001)-Single-Speed Shown
A01377
AUXILIARY LIMIT
DOOR SWITCH
(ILK-I)
POWER JUNCTION BOX
RELOCATED HERE
SECONDARY AUXILIARY
LIMIT SWITCH (ALS-S)
MAIN 24-V
TRANSFORMER
MAIN BLOWER ACCESS
PANEL DOOR SWITCH
SECONDARY 24-V
TRANSFORMER
MAIN AUXILIARY
LIMIT SWITCH
(ALS-M)
8″ TYP
TWINNING KIT
RELAY (TKR)
SECONDARY BLOWER ACCESS
PANEL DOOR SWITCH
UNUSED CONDENSATE
DRAIN LINE HOLES
WITH SNAP
BUSHING INSTALLED
Fig. 30—External Extension Harness (Back-to-Back Application)
A02225
Unused condensate
drain location
External Extension
—32—
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