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1. Turn gas and power to furnace to OFF.
2. Remove control and blower access doors.
3. Disconnect vent connector from furnace flue collar.
4. Disconnect internal vent pipe and enclosure on downflow
furnaces only.
a. Remove vent pipe enclosure cover.
b. Disconnect and remove short piece of vent pipe from
within furnace.
NOTE: Vent pipe is SCREWED and RTV sealed to relief box.
c. Remove vent pipe enclosure by removing screw in upper
back. Push bottom side backward to release tabs.
5. Remove 2 screws that secure relief box. (See Fig. 5 or 6.)
6. Disconnect wires to the following components. Mark wires
to aid in reconnection of:
a. Draft safeguard switch.
b. Inducer motor.
c. Pressure switch(es).
d. Limit overtemperature switch(es).
e. Gas valve.
f. Hot surface ignitor.
g. Flame-sensing electrode.
h. Flame rollout switch(es), if applicable.
7. Remove complete inducer assembly and relief box from
furnace.
8. Remove screws that secure flue collector box to center
panel. Be careful not to damage collector box.
9. Remove cell outlet plates.
IMPORTANT: Replace screws in center panel before cleaning.
10. Remove burner assembly and cell inlet plates.
IMPORTANT: Replace screws in center panel before cleaning.
NOTE: Be very careful when removing burner assembly to avoid
breaking ignitor. See Fig. 7 for correct ignitor location.
11. Using field-provided small wire brush, steel spring cable,
reversible electric drill, and vacuum cleaner, clean cells as
follows:
a. Assemble wire brush and steel spring cable.
(1.) Use 48 in. of 1/4-in. diameter high-grade steel
spring cable (commonly known as drain clean-out
or Roto-Rooter® cable).
(2.) Use 1/4-in. diameter wire brush (commonly known
as 25-caliber rifle cleaning brush).
NOTE: The materials needed in items (1.) and (2.) can usually be
purchased at local hardware stores.
(3.) Insert twisted wire end of brush into end of spring
cable, and crimp tight with crimping tool or strike
with ball-peen hammer. TIGHTNESS IS VERY
IMPORTANT.
(4.) Remove metal screw fitting from wire brush to
allow insertion into cable.
b. Clean each heat exchanger cell.
(1.) Attach variable-speed, reversible drill to end of
spring cable (end opposite brush).
(2.) Insert brush end of cable into upper opening of cell
and slowly rotate with drill. DO NOT force cable.
Gradually insert at least 36 in. of cable into 2 upper
passes of cell. (See Fig. 8.)
(3.) Work cable in and out of cell 3 or 4 times to obtain
sufficient cleaning. DO NOT pull cable with great
force. Reverse drill and gradually work cable out.
(4.) Insert brush end of cable in lower opening of cell,
and proceed to clean 2 lower passes of cell in same
manner as 2 upper passes.
(5.) Repeat foregoing procedures until each cell in
furnace has been cleaned.
(6.) Using vacuum cleaner, remove residue from each
cell.
(7.) Using vacuum cleaner with soft brush attachment,
clean burner assembly.
(8.) Reinstall cell outlet plates and screws FIRST; then,
reinstall cell inlet plates and burner assembly. Care
must be exercised to center burners in cell openings.
12. Remove old sealant from center panel and collector box
flange and apply new sealant to collector box flange and
reinstall on center panel, making sure all screws are secure.
Fig. 7—Position of Ignitor to Burner
A93347
BURNER
IGNITOR
11
32
"
7
8
"
C
L
C
L
IGNITOR
ASSEMBLY
CELL
PANEL
BURNER
13
32
"
HOT
SURFACE
IGNITOR
ASSEMBLY
Fig. 8—Cleaning Heat Exchanger Cell
A91252
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