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FIGURE 1
G27M
PARTS IDENTIFICATION
VENT ADAPTER
CABINET TOP CAP
G27M
CABINET
CABINET
BOTTOM
HEAT EXCHANGER
ASSEMBLY
BURNER BOX
ASSEMBLY
BLOWER ASSEMBLY
COMBUSTION AIR
BLOWER
FLUE BOX
SECONDARY
LIMIT CONTROLS
FRONT LOUVERED
PANEL
SureLight
IGNITION
CONTROL
BOARD
TRANSFORMER
PRESSURE
SWITCHES
NOx
TURBULATOR
(For G27MX units only)
TWO–STAGE
CONTROL
BOARD
CABINET
BOTTOM
CAP
DOOR INTERLOCK SWITCH
I–UNIT COMPONENTS (Figure 1)
G27M unit components are shown in figure 1. The
blower controls, gas valve and burners can be accessed
by removing the front access panel. A separate blower
access door is located behind the front access panel.
Electrical control components are mounted on the
blower access door. Units are factory–equipped with
bottom return air panels
A–Blower Door Components
The SureLight integrated ignition and blower control is lo-
cated on the outside surface of the blower access door
along with the unit transformer (T1), the two–stage con-
trol and a door interlock switch (S51). Jackplugs allow the
blower door to be removed for blower service.
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 40VA with a 120V primary and a 24V
secondary. The transformer is protected by a 3.0 amp
circuit breaker.
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.
3– SureLight Ignition System (A3)
All G27M units are equipped with the Lennox Sure –
Light ignition system. The system consists of an igni-
tion control board (figure 2) and ignitor (figure 3). The
board and ignitor work in combination to ensure fur-
nace ignition and ignitor durability. The SureLight in-
tegrated board controls all major furnace operations.
The board also features two LED lights for trouble-
shooting and two accessory terminals. See table 1 for
troubleshooting diagnostic codes. Table 2 and 3 show
jack plug terminal designations. Units equipped with
the SureLight board can be used with either electronic
or electro–mechanical thermostats without modifica-
tion. The SureLight ignitor is made of durable silicon–
nitrite. Ignitor longevity is also enhanced by voltage
ramping by the control board. The board finds the low-
est ignitor temperature which will successfully light
the burner, thus increasing the life of the ignitor.
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.
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