LGA/LCA/LHA - lennox

3−Burner Assembly (Figure 22)
The burners are controlled by the spark electrode, flame sensing
electrode, gas valve and combustion air inducer. The spark
electrode, flame sensing electrode and gas valve are directly
controlled by ignition control. Ignition control and combustion
air inducer is controlled by main control panel A55.
Burners
All units use inshot burners (see figures 22 and 23). Burners
are factory set and do not require adjustment. A peep
hole with cover is furnished in the heating access
panel for flame viewing. Always operate the unit with
the access panel in place.
Burners can be removed individually for service.
Burner maintenance and service is detailed in the
SERVICE CHECKS sections of this manual.
TYPICAL GAS BURNER ASSEMBLY
BURN-
ERS
BURNER
SUPPORT
ORIFICE
SENSOR
BURNER
SUPPORT
CAP
FIGURE 22
Orifice
Each burner uses an orifice which is precisely matched to
the burner input. The orifice is threaded into the burner
manifold. The burner is supported by the orifice and will
easily slide off for service.
NOTE−Do not use thread sealing compound on the orifices.
Using thread sealing compound may plug the orifices.
Each orifice and burner are sized specifically to the unit.
Refer to Lennox Repair Parts Listing for correct sizing information.
TYPICAL GAS MANIFOLD ASSEMBLY
ORIFICE
MANIFOLD
FIGURE 23
BURNERS
Page 50
NOTE−In primary and secondary high temperature limits
S10, S99, S21, and S100 the ignition circuits in both gas
heat sections one and two are immediately de−energized
when terminals 1−3 open and the indoor blower motor
is immediately energized when terminals 1−2
close. This is the primary and secondary safety shut−
down function of the unit.
4−Primary High Temperature Limits
S10 & S99
S10 is the primary high temperature limit for gas heat section
one, while S99 is the primary high temperature limit for gas
heat section two. S10 is located in the blower compartment
and is mounted on the end of the blower support panel which
divides the blower compartment from the heating compartment
(see figure 17). S99 is located on the blower support
panel which separates the second gas heat section from the
outdoor condenser section (see figure 17).
Figure 17 also shows the location of S10 and S99 in
LGA240H units. S10 and S99 are located on the drip shield
behind the blower housing. In this location S10 and S99
serve as both primary and secondary limt.
Primary limit S10 is wired to the main control panel A55
which energizes burner 1 control (A3), while primary limit S99
is wired to the gas 2 panel A58 which energizes burner 2
control (A12). Its N.C. contacts open to de−energize the
ignition control when excessive temperature is reached in the
blower compartment. At the same time, the N.O. contacts of
S10 and S99 close energizing the blower relay coil K3 through
control A55. If either limit trips the blower will be energized.
Limit set points are factory set and cannot be adjusted. If limit
must be replaced same type and set point must be used. See
Lennox Repair Parts Handbook .
5−Secondary High Temperature Limits
S21 & S100
S21 is the secondary high temperature limit for heat section
one, while S100 is the secondary high temperature
limit for heat section two. Like the primary limits, the secondary
limits are located in the blower compartment.
S21 and S100 are mounted on top of the blowers (see
figure 17).
Secondary limit S21 is also wired to the main control
panel A55, while secondary limit S100 is wired to the gas
2 panel A58. The secondary limits function in the same
manner as the primary limits, but are factory set to actuate
at different temperatures. The N.O. contacts of both
S21 and S100 are connected to the blower relay coil K3
through control A55. If either limit trips the blower will be
energized. All limits used are SPDT N.C. auto−reset limits.
Limit set points are factory set and cannot be adjusted. If limit
must be replaced same type and set point must be used. See
Lennox Repair Parts Handbook .