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C- Heating Components
1. Ignitor
The SureLight
®
ignitor is made of durable silicon nitride.
Ignitor longevity is enhanced by controlling voltage to the
ignitor. The integrated control provides a regulated 120
volts to the ignitor for a consistent ignition and long ignitor
life. Ohm value should be 39 to 70. See FIGURE 14 for
ignitor location and FIGURE 15 for ignitor check out.
NOTE - The SL280DFV(X) furnace contains electronic
components that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.
2. Flame Sensor
A ame sensor is located on the left side of the burner
support. See FIGURE 14. The sensor is tip protrudes into
the ame envelope of the left-most burner. The sensor
can be removed for service without removing any part of
the burners. During operation, ame is sensed by current
passed through the ame and sensing electrode. The
SureLight control allows the gas valve to remain open as
long as ame signal is sensed. To check ame sense sig-
nal use the push-button found on the integrated control
and go to Field Test Mode. The menu will display the ame
signal. See TABLE 15 for ame signal.
TABLE 15
Flame Signal in Microamps
Normal Low Drop Out
2.6 or greater 2.5 or less
1.1
3. Gas Valve
The valve (FIGURE 17 or FIGURE 18) is internally redun-
dant to assure safety shut-o. If the gas valve must be
replaced, the same type valve must be used.
24VAC terminals and gas control knob are located on the
valve. A wire harness connects the terminals from the gas
valve to the electronic ignition control. 24V applied to the
terminals energizes the valve.
Inlet and outlet pressure taps are located on the valve. A
regulator adjustment screw is located on the valve.
LPG change over kits are available from Lennox. Kits in-
clude burner orices and a gas valve.
4. Flame Rollout Switches (S47)
Flame rollout switch is a high temperature limit located on
top of the burner box, one on each side.- See FIGURE
14. The limit is a N.C. SPST manual-reset limit connected
in series with the secondary limit S21. When S47 senses
rollout, the circuit breaks and the ignition control immedi-
ately stops ignition and closes the gas valve. Rollout can
be caused by a blocked heat exchanger, ue or lack of
combustion air.The switch is factory set to trip (open) at
210°F and cannot be adjusted. The switch can be manual-
ly reset. To manually reset a tripped switch, push the reset
button located on the control.
5. Burners
All units use inshot burners. Burners are factory set and
require no adjustment. Always operate the unit with the
burner box front panel in place. Each burner uses an
orice (see TABLE 20 for orice size) that is precisely
matched to the burner input. Burners can be removed as
a one piece assembly for service. If burner assembly has
been removed, it is critical to align center of each burner
to the center of the clamshell when re-installing. See more
detail in Section VI- MAINTENANCE sub-section A- Heat
Exchanger and Burners.
6. Primary Limit Control (S10)
The primary limit (S10) is located in the heating vestibule
panel. When excess heat is sensed in the heat exchanger,
the limit will open. If the limit is open, the furnace control
energizes the supply air blower and closes the gas valve.
The limit automatically resets when unit temperature re-
turns to normal. The switch must reset within three min-
utes or the SureLight control will go into Watch guard for
one hour. The switch is factory set and cannot be adjust-
ed. The switch may have a dierent set point for each unit
model number. See Lennox Repair Parts Handbook if limit
switch must be replaced,
7. Secondary Limit Controls (S21)
The secondary limit (S21) is located in the blower com-
partment. See FIGURE 7. When excess heat is sensed in
the blower compartment, the limit will open. If the limit is
open, the furnace control energizes the supply air blower
and closes the gas valve. The limit automatically resets
when unit temperature returns to normal. The switch must
reset within three minutes or the SureLight control will go
into Watch guard for one hour. The switch is factory set
and cannot be adjusted.
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