Lennox ML193UHE Series Unit Information page 47

Condensate Hose Screens
Hose
FIGURE 60
Cleaning Heat Exchanger
If cleaning the heat exchanger becomes necessary, follow
the below procedures and refer to figure 1 when disas-
sembling unit. Use papers or protective covering in front of
furnace 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.
8 - Remove the clean-out cap on trap and drain.
Replace cap.
9 - Disconnect condensate
condensate trap. Remove condensate trap (it may
be necessary 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.
10 - Disconnect condensate drain tubes from flue collar.
Remove screws that secures flue collar in place.
Remove flue collar. It may be necessary to cut the
exiting exhaust pipe for removal of the fitting.
11 - Loosen two clamps from flexible no-hub exhaust
collar.
12 - Disconnect the 2-pin plug from the combustion air
inducer. Remove screws which secure combustion
air inducer to collector box. Remove combustion air
inducer assembly. Remove ground wire.
13 - Mark and disconnect all combustion air pressure
tubing from cold end header collector box.
14 - Mark and remove wires from pressure switch.
Remove pressure switch. Keep tubing attached to
pressure switch.
15 - Remove electrical junction box from the side of the
furnace.
16 - Remove blower access panel.
Hose
drain line from the
Page 47
17 - 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.
18 - Remove the primary limit from the vestibule panel.
19 - Remove top cap screws to allow top cap to be
tilted upward to allow clearance for removing heat
exchanger.
20 - Remove two screws from the front cabinet flange
at the blower deck. Spread cabinet sides slightly to
allow clearance for removal of heat exchanger.
21 - Remove screws along vestibule sides and bottom
which secure vestibule panel and heat exchanger
assembly to cabinet. Remove two screws from
blower rails which secure bottom heat exchanger
flange.
22 - Remove 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.
26 - Remove the indoor blower to view this area through
the blower opening.
27 - Re-secure the supporting screws along the
vestibule sides.
28 - Reinstall blower assembly and reinstall two screws
through rails.
29 - Reinstall cabinet screws on front flange at blower
deck.
30 - Reinstall screws securing top cap.
31 - Reinstall the primary limit on the vestibule panel.
32 - Route heating component wiring through hole in
blower deck and reinsert strain relief bushing.
33 - Reinstall pressure switch and reconnect pressure
switch wiring.
34 - Carefully connect combustion air pressure switch
hosing from pressure switch to proper stubs on cold
end header collector box.
35 - Reinstall 1/2" NPT (if removed) in the cold end
header box. Reconnect drain tubing to collector
box.
36 - Reinstall condensate
condensate drain line to the condensate trap.
37 - Reinstall electrical junction box.
38 - 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.
trap pipe. Reconnect