46
441 01 2121 01
force cable. Gradually insert cable into upper
pass of cell. (See Figure 55)
(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 burner inlet open-
ing of cell, and proceed to clean 2 lower
passes of cell in same manner as upper pass.
(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 attach-
ment, clean burner assembly.
(8.) Clean flame sensor with fine steel wool.
(9.) Install NOx baffles (if removed).
Figure 54 − Cleaning Heat Exchanger Cell
A91252
(10.) Reinstall burner assembly. Center burners in
cell openings.
10. Remove old sealant from cell panel and collector box
flange.
11. Spray releasing agent on the heat exchanger cell panel
where collector box assembly contacts cell panel.
NOTE: A releasing agent such as a vegetable oil cooking
spray that does not contain corn oil, canola oil, halogenated
hydrocarbons or aromatic content, which may prevent an
inadequate seal from occuring, and RTV sealant such as
G.E. RTV 162, G.E. RTV 6702, or Dow−Corning RTV 738
sealant are required. DO NOT substitute any other type of
RTV sealant.
12. Apply new sealant to flange of collector box and attach
to cell panel using existing screws, making sure all
screws are secure.
13. Reconnect wires to the following components (Use
connection diagram on wiring label, if wires were not
marked for reconnection locations.):
a. Draft safeguard switch.
b. Inducer motor.
c. Pressure switches.
d. Limit overtemperature switch.
e. Gas valve.
f. Hot surface igniter.
g. Flame−sensing electrode.
h. Flame rollout switches.
14. Reinstall internal vent pipe, if applicable.
15. Reinstall vent connector on furnace vent elbow. Se-
curely fasten vent connector to vent elbow with 2 field−
supplied, corrosion−resistant, sheet metal screws loc-
ated 180 apart.
16. Replace blower access door only if it was removed.
17. Set thermostat above room temperature and check fur-
nace for proper operation.
18. Verify blower airflow and speed changes between
heating and cooling.
19. Check for gas leaks.
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in personal
injury, death, and/or property damage.
Never purge a gas line into a combustion chamber.
Never test for gas leaks with an open flame. Use a
commercially available soap solution made
specifically for the detection of leaks to check all
connections.
!
WARNING
Sequence of Operation
NOTE: Furnace control must be grounded for proper
operation or else control will lock out. Control is grounded
through green/yellow wire routed to gas valve and burner box
screw. Using the schematic diagram in Figure 56, follow the
sequence of operation through the different modes. Read and
follow the wiring diagram very carefully.
NOTE: If a power interruption occurs during a call for heat
(W/W1 or W/W1−and−W2), the control will start a 90−second
blower−only ON period two seconds after power is restored, if
the thermostat is still calling for gas heating. The amber LED
light will flash code 1+2 during the 90−second period, after
which the LED will flash a heartbeat (bright−dim), as long as
no faults are detected. After the 90−second period, the
furnace will respond to the thermostat normally.
The blower door must be installed for power to be conducted
through the blower door interlock switch ILK to the furnace
control CPU, transformer TRAN, inducer motor IDM, blower
motor BLWM, hot−surface igniter HSI, and gas valve GV.
1. Two−Stage Heating (Adaptive Mode) with Single−
Stage Thermostat
See Figure 25 thermostat connections
NOTE: The low−heat only switch SW1−2 selects either the
low−heat only operation mode when ON, (see item 2. below)
or the adaptive heating mode when OFF in response to a call
for heat. (See Table 10) When the W2 thermostat terminal is
energized it will always cause high−heat operation when the
R−to−W circuit is closed, regardless of the setting of the
low−heat only switch. This furnace can operate as a
two−stage furnace with a single−stage thermostat because
the furnace control CPU includes a programmed adaptive
sequence of controlled operation, which selects low−heat or
high−heat operation. This selection is based upon the stored
history of the length of previous gas−heating periods of the
single−stage thermostat.
The furnace will start up in either low− or high−heat. If the
furnace starts up in low−heat, the control CPU determines the
low−heat on−time (from 0 to 16 minutes) which is permitted
before switching to high−heat.
If the power is interrupted, the stored history is erased and
the control CPU will select low−heat for up to 16 minutes and
then switch to high−heat, as long as the thermostat continues
to call for heat. Subsequent selection is based on stored
history of the thermostat cycle times.
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