14. Go to PROCEDURE 2A for Single Stage Furnaces or PROCEDURE 2B for Two Stage Furnaces.
B.
Upflow/Downflow, Back-to-Back Position
Refer to Fig. 3 and Table 2 for appearance and dimensional drawing of twinned furnaces and their connection locations.
1. Select 2 identical heating and airflow furnaces. (See Table 2.)
2. Remove outer door and blower access door.
3. Remove bottom closure panels from both furnaces. (See Fig. 4.)
a. Lay furnaces on back or sides.
b. Remove 2 screws from bottom front panel.
c. Rotate front panel downward to remove.
d. Remove bottom closure panel and discard.
e. Reinstall bottom front panel.
f. Stand furnaces upright.
4.
a. For upflow applications:
Bottom return air usage is required as part of any upflow return air configuration. If additional return air is to enter 1 side of each furnace,
in addition to bottom return air, cut open 1 entire return-air opening in appropriate side of each furnace. (See Fig. 2.)
WARNING: UNIT DAMAGE AND FIRE HAZARD
Failure to follow this warning could result in unit damage, fire, personal injury or death.
DO NOT use the side of the furnace for return-air duct connections in the downflow position, as limit cycling will occur.
b. For downflow applications:
Return air can only be connected to bottom opening of furnace. A common return air plenum is required for proper auxiliary limit switch
operation. (See Fig. 3.)
5. Apply 2 factory-supplied foam strips to the back of each furnace. Locate strips equal distance from top and bottom as shown in Fig. 5. Trim
off excess material.
6. Determine which side of furnace will be used to route external extension harness. Remove 7/8-in. diameter accessory hole knockouts in
blower compartment side selected to attach harness to. (See Fig. 3.)
7. Bend or remove the supply flanges as required for upflow or downflow installation. Refer to the furnace installation instructions for
complete details.
8. Position furnaces back-to-back on return-air plenum, supply air plenum or evaporator coil casing. Adjust and shim each furnace to align
both furnaces.
NOTE:
External extension harness cannot be used on the same side of the furnace that the return air ducts connect to. Locate harness on opposite
side of furnace when side return air is used.
9. Drill two 1/8-in. holes, approximately 1 in. below discharge flange, from inside top of discharge opening and through both furnaces. (Similar
to Fig. 6.)
Drill two 1/8-in. holes, approximately 1 in. below return air flange, from inside top of return air opening and through both furnaces. (Similar
to Fig. 7.)
10. Drive 1 factory-supplied No. 6 X 3/4-in. LG screw through each hole and tighten until furnaces are secure and foam strips have sealed gap
between furnaces.
11. Connect return- and supply-air ducts to furnaces. Seal duct connections to prevent air leakage.
12. Move 115-v junction box JB in either furnace from left-hand side to right-hand side if required. Refer to furnace installation instructions
for complete details.
A02232
Fig. 6—Attaching Furnaces Together at Discharge Opening
A02219
Fig. 7—Attaching Furnaces Together at Return Air Opening
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