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5. Install Auxiliary Blower Door Interlock Switch, ILK-1 on Secondary furnace:
a. Measure along the left edge of the furnace casing, 5 inches down from blower shelf.
b. Drill a 3/16
″
clearance hole through front edge of furnace casing.
c. Insert blower door switch mounting tab behind front edge of furnace casing.
d. Secure blower door switch through casing with special flat head screw included with kit.
e. Secure auxiliary door switch ILK-1 using factory-supplied shallow head screw.
f. Connect 2-Wire Secondary Harness to 2-wire Main Harness that was routed through furnace casings.
g. If extension harness was installed, 2-wire Secondary Harness from Secondary to Main Extension Harness.
NOTE:
If Extension Harness will not plug in to L/H and R/H furnaces, extension harness is installed backward. Remove extension harness and
re-install in correct orientation.
6. Select identical blower motor speed taps at control center motor connectors in both furnaces.
CAUTION: UNIT DAMAGE HAZARD
Failure to select identical blower speed taps in both furnaces can result in overheating of furnace components and possible loss of
furnace operation and damage to the furnaces.
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. See Fig. 13.
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. 14.)
NOTE:
This application allows only the LH furnace to operate for first-stage heat mode or both furnaces to operate 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 Single-Stage Heat
with Single-Stage Gas Heat Thermostat, then modify TKR wiring as follows:
a. Disconnect TKR white wire labeled W from the LH furnace control thermostat connection W.
b. Cut off terminal of TKR white wire labeled W and strip 1/4 in.
c. Connect 2-stage thermostat W2 connection to TKR white wire labeled W.
Fig. 10B—Holes Drilled in Blower Housing
A02220
Align TKR Relay along edge of control
board. Mark holes in control board
mounting bracket and drill screw holes
using 1/8” drill bit. Secure relay to
control board mounting bracket using
factory-supplied screws.
—14—