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I-UNIT COMPONENTS (Figures 1, 2, 3)
G24M unit components are shown in figure 1. The blower
controls, gas valve and burners can be accessed by reĆ
moving the front access panel. A separate blower access
door is located behind the front access panel. Electrical
control components are mounted to the blower access
door.
G24M units are factory equipped with bottom return air panels
in place. The panels are designed to be field removed as reĆ
quired for bottom air return. Indentations on side of units,
show where side return opening should be cut during installaĆ
tion.
A-Blower Door Components (Figure 4)
Electrical burner control and blower control components
are located on the outside surface of the blower access
door. Jackplugs allow the blower door to be easily reĆ
moved for blower service.
Located on the blower door are the unit transformer (T1),
the furnace control (A3) and door interlock switch (S51).
Furnace control (A3) combines the function of a burner
ignition control and blower control.
1- Control Transformer (T1)
A transformer located on the blower door provides power
to the low voltage section of the unit. Transformers on all
models are rated 30VA with a 120V primary and a 24V secĆ
ondary.
2-Door Interlock Switch (S51)
A door interlock switch rated 16A at 125VAC is located on
the blower access door. The switch is wired in series with
line voltage. When the blower door is removed the unit will
shut down.
DANGER
Shock hazard.
Disconnect power before servicing. Control is not
field repairable. If control is inoperable, simply
replace entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.
3- SureLight Ignition System (A3)
Late Model G24M Units
Late model G24M units are equipped with the Lennox
SureLight ignition system. The system consists of ignitor
(figure 5) and ignition control board (figure 6 with control
terminal designations in table 1). The board and ignitor
work in combination to ensure furnace ignition and ignitor
durability. The SureLight integrated board controls all
major furnace operations. The board also features two
LED lights for troubleshooting and two accessory termiĆ
nals rated at (4) four amps. See table 2 for troubleshootĆ
ing diagnostic codes. Table 3 and 4 show jack plug termiĆ
nal designations. Units equipped with the SureLight
board can be used with either electronic or electro-meĆ
chanical thermostats without modification. The SurĆ
eLight ignitor is made of durable silicon-nitride. Ignitor
longevity is also enhanced by voltage ramping by the
control board. The board finds the lowest ignitor temperaĆ
ture which will successfully light the burner, thus increasĆ
ing the life of the ignitor.
a-flame sensor
The flame sensor uses flame rectification to sense comĆ
bustion. During operation, flame is sensed by current
passed through the flame and sensing electrode. Figure 7
shows the gap between tip of the electrode and the burner
surface.
FIGURE 5
SURELIGHT IGNITOR BURNER ASSEMBLY
FLAME SENSOR
FLAME RETENTION RING
UPPER BURNER
MOUNTING RAIL
ORIFICE
SURELIGHT IGNITOR