Page 16
C- Heating Components
1. Ignitor
The ignitor is made of durable silicon nitride. Ignitor lon-
gevity 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 12 for ignitor
location.
NOTE - This 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 12. The sensor 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. See TABLE 6 for ame
signal.
TABLE 6
Flame Signal in Microamps
Normal Low Drop Out
1.5 or greater 1.0 or less 0.5
3. Gas Valve
The valve (gure 50) is internally redundant 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
12. The limit is a N.C. SPST manual-reset limit. When
S47 senses rollout, the circuit breaks and the ignition con-
trol immediately 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 manually 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 ori-
ce (see table 21 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.
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.
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