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Two-Stage Heat with Single-Stage Gas-Heat Thermostat (Field Supplied) (See Fig. 15.)
NOTE:
This application allows both furnaces to operate as 1 furnace in gas heat mode as determined by single-stage thermostat operation. Both
furnaces operate in heating mode simultaneously. See furnace Installation, Start-Up, and Operating Instructions for further details on this heating
mode.
1. Install harness labeled “Main Furnace” with TKR on L/H Furnace:
The Main Harness includes the TKR relay and Auxiliary Limit switch on the harness. The harness is also tagged “Main Furnace” near the
ends of the plug connector.
a. Secure relay of TKR harness assembly to LH furnace control mounting bracket using 2 factory-supplied screws. Two new screw holes
will have to be drilled using a 1/8-inch drill bit. See Fig. 10B for location of holes to be drilled.
b. Connect TKR white wire labeled W from TKR to LH furnace control thermostat connection W/W1.
c. Connect TKR black wire labeled C from TKR to LH furnace control thermostat connection C
OM
24V.
d. Connect yellow wire labeled TEST to LH furnace control TEST/TWIN terminal.
e. If Extension Harness was used, connect 4-wire harness to Extension Harness.
f. Turn LHT set-up switch on L/H control board to “OFF.” (See Fig. 12.)
g. Turn LHT set-up switch on R/H control board to “ON.”
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.
2. Install Auxillary Limit Switch (ALS-M) on L/H furnace:
a. Drill 1/8-in. hole in blower housing 12 in. below blower shelf. (See Fig. 11.)
b. Position ALS-M so reset button faces front of furnace.
c. Secure bracket to blower housing using a factory-supplied screw.
d. Disconnect red transformer wire from LH furnace control SEC-1 connection.
e. Connect red transformer wire connector to ALS-M wire connector PL7 labeled TRAN.
f. Connect ALS-M orange wire connector labeled DOOR SWITCH or SEC 1 to LH furnace control SEC-1 terminal.
g. If Extension Harness was used, connect 2-wire harness to Extension Harness
3. Install Secondary 4-wire harness on R/H furnace:
The Secondary Harness includes the Auxiliary Door Switch and Auxiliary Limit Switch. The harness is also tagged “Secondary Furnace” near the
plug ends of the harness.
a. Connect red wire labeled R-Secondary to RH furnace control thermostat connection R.
b. Connect white wire labeled W-Secondary to RH furnace control thermostat connection W/W1.
c. Connect black wire labeled C-Secondary to RH furnace control thermostat connection C
OM
24V.
d. Connect yellow wire labeled TEST SECONDARY to RH furnace control TEST/TWIN terminal.
e. If the furnaces are side-by-side, route loose ends of 4-wire harness from Secondary furnace to Main furnace through snap bushings
previously installed between furnaces.
f. Connect Secondary 4-wire harness into 4-wire Main harness.
g. If Extension Harness was installed, connect 4-wire Secondary Harness to the Extension Harness.
4. Install Auxiliary Limit Switch, ALS-S on Secondary furnace:
a. Drill 1/8-in. hole in blower housing 12 in. below blower shelf. (See Fig. 11.)
b. Position ALS-S with terminals facing front of furnace.
c. Secure bracket to blower housing using factory-supplied screw.
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 from Secondary to Main furnace casings.
g. If extension harness was installed, 2-wire Secondary Harness to 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.
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