Lennox EL280DF Series Unit Information page 10

B- Indoor Blower
1. Blower Motors and Capacitors
All EL280DF units use direct drive blower motors. All mo­
tors are 120V permanent split capacitor motors to ensure
maximum efficiency. Ratings for capacitors will be on mo­
tor nameplate. See SPECIFICATIONS section for motor
specifications.
2. Secondary Limit Control (S21)
The secondary limit (S21) is located in the blower compart­
ment. See figure 1. 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.
C- Heating Components
1. Ignitor
®
The SureLight ignitor is made of durable silicon nitride. Ig­
nitor longevity is enhanced by controlling voltage to the ig­
nitor. 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 7 for ignitor loca­
tion and figure 8 for ignitor check out.
NOTE - The EL280DF furnace contains electronic compo­
nents that are polarity sensitive. Make sure that the furnace
is wired correctly and is properly grounded.
2. Flame Sensor
A flame sensor is located on the left side of the burner sup­
port. See figure 7. The sensor protrudes into the flame en­
velope of the left-most burner. The sensor can be removed
for service without removing any part of the burners. During
operation, flame is sensed by current passed through the
flame and sensing electrode. The SureLight control allows
the gas valve to remain open as long as flame signal is
sensed. A microamp DC meter is needed to check the
flame signal on the integrated control. See figure 9 and
table 5 for flame signal check and measurement.
3. Gas Valve
The two-stage gas valve (figure 11) is internally redundant
to assure safety shut-off. If the gas valve must be replaced,
the same type valve must be used.
24VAC terminals and ON/OFF switch 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 orifices.
4. Flame Rollout Switches (S47)
The EL280DF is equipped with a single rollout switch. See
figure 7 for location. The limit is a N.C. SPST manual‐reset
limit. When S47 senses rollout, the circuit breaks and the
ignition control immediately stops ignition and closes the
gas valve. Rollout can be caused by a blocked heat ex­
changer, flue or lack of combustion air. The switches are
factory set to trip (open) at 210°F and cannot be adjusted.
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 re­
quire no adjustment. Always operate the unit with the burn­
er box front panel in place. Each burner uses an orifice that
is precisely matched to the burner input. Burners can be re­
moved as a one piece assembly for service. If burner as­
sembly has been removed, it is critical to align center of
each burner to the center of the clamshell when re-instal­
ling.
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 en­
ergizes 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 Watchguard for one hour.
The switch is factory set and cannot be adjusted. The
switch may have a different set point for each unit model
number. See Lennox Repair Parts Handbook if limit switch
must be replaced,
Page 10