Lennox ML193UH045P36B Unit Information page 45

Cleaning Heat Exchanger
If cleaning the heat exchanger becomes necessary, follow
the below procedures and refer to figure 1 when disassem­
bling unit. Use papers or protective covering in front of fur­
nace while removing heat exchanger assembly.
1 - Turn off electrical and gas supplies to the furnace.
2 - Remove the burner access panel.
3 - Mark all gas valve wires and disconnect them from
valve.
4 - Remove gas supply line connected to gas valve.
5 - Remove sensor wire from flame sensor. Disconnect
2‐pin plug from the ignitor.
6 - Disconnect wires from flame roll-out switches.
7 - Remove four burner assembly screws at the vestibule
panel and remove gas valve /manifold and burner box
as a single unit.
NOTE - If necessary, clean burners at this time. Follow
procedures outlined in Burner Cleaning section.
9 - Remove the clean-out cap on trap and drain. Replace
cap.
10 - Disconnect condensate drain line from the conden­
sate trap. Remove condensate trap (it may be neces­
sary to cut drain pipe). Remove the 1/2" NPT fitting
from the cold end header box. Disconnect drain tubes
from cold end header collector box.
11 - Disconnect condensate drain tubes from flue collar.
Remove screws that secures flue collar in place. Re­
move flue collar. It may be necessary to cut the exiting
exhaust pipe for removal of the fitting.
12 - Loosen two clamps from flexible no-hub exhaust col­
lar.
13 - Disconnect the 2‐pin plug from the combustion air in­
ducer. Remove screws which secure combustion air
inducer to collector box. Remove combustion air in­
ducer assembly. Remove ground wire.
14 - Mark and disconnect all combustion air pressure tub­
ing from cold end header collector box.
15 - Mark and remove wires from pressure switch. Re­
move pressure switch. Keep tubing attached to pres­
sure switch.
16 - Remove electrical junction box from the side of the fur­
nace.
17 - Remove blower access panel.
18 - Mark and disconnect any remaining wiring to heating
compartment components. Disengage strain relief
bushing and pull wiring and bushing through the hole
in the blower deck.
19 - Remove the primary limit from the vestibule panel.
20 - Remove top cap screws to allow top cap to be tilted up­
ward to allow clearance for removing heat exchanger.
21 - Remove two screws from the front cabinet flange at
the blower deck. Spread cabinet sides slightly to allow
clearance for removal of heat exchanger.
22 - Remove screws along vestibule sides and bottom
which secure vestibule panel and heat exchanger as­
sembly to cabinet. Remove two screws from blower
rails which secure bottom heat exchanger flange. Re­
move heat exchanger from furnace cabinet.
23 - Back wash heat exchanger with soapy water solution
or steam. If steam is used it must be below 275°F
(135°C) .
24 - Thoroughly rinse and drain the heat exchanger. Soap
solutions can be corrosive. Take care to rinse entire
assembly.
25 - Reinstall heat exchanger into cabinet making sure that
the rear baffle of the heat exchanger assembly is
nested under the support located at the rear of the
cabinet. Remove the indoor blower to view this area
through the blower opening.
26 - Re‐secure the supporting screws along the vestibule
sides.
27 - Reinstall blower assembly and reinstall two screws
through rails.
28 - Reinstall cabinet screws on front flange at blower
deck.
29 - Reinstall screws securing top cap.
30 - Reinstall the primary limit on the vestibule panel.
31 - Route heating component wiring through hole in blow­
er deck and reinsert strain relief bushing.
32 - Reinstall pressure switch and reconnect pressure
switch wiring.
33 - Carefully connect combustion air pressure switch hos­
ing from pressure switch to proper stubs on cold end
header collector box.
34 - Reinstall 1/2" NPT (if removed) in the cold end header
box. Reconnect drain tubing to collector box.
35 - Reinstall condensate trap pipe. Reconnect conden­
sate drain line to the condensate trap.
36 - Reinstall electrical junction box.
37- Reinstall the combustion air inducer and flexible no
hub connector. Reconnect the 2-pin plug to the wire
harness.
39 - Reconnect drain tubes between flue collar and cold
end header box.
40 - Secure burner assembly to vestibule panel using four
existing screws. Burners are self aligning to center
of clam shells.
41 - Reconnect gas supply line to gas valve.
42 - Reconnect flame roll-out switch wires.
43 - Reconnect sensor wire and reconnect 2-pin plug from
ignitor.
44 - Reconnect wires to gas valve.
45 - Replace the blower compartment access panel.
46 - Refer to instruction on verifying gas and electrical con­
nections when re-establishing supplies.
47 - Follow lighting instructions to light and operate fur­
nace for 5 minutes to ensure that heat exchanger is
clean and dry and that furnace is operating properly.
48 - Replace heating compartment access panel.
Page 45