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I−UNIT COMPONENTS
G40DF(X) unit components are shown in figure 1. The gas
valve, combustion air inducer and burners can be ac-
cessed by removing the burner access panel. Electrical
components are in the control box (figure 2) found in the
blower section.
CAUTION
Electrostatic discharge can affect electronic
components. Take precautions during furnace
installation and service to protect the furnace’s
electronic controls. Precautions will help to
avoid control exposure to electrostatic dis-
charge by putting the furnace, the control and
the technician at the same electrostatic poten-
tial. Neutralize electrostatic charge by touching
hand and all tools on an unpainted unit surface,
such as the gas valve or blower deck, before per-
forming any service procedure.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
1. Control Transformer (T1)
A transformer located in the control box provides power to
the low voltage section of the unit. Transformers on all
models are rated 40VA with a 120V primary and a 24V sec-
ondary.
2.Door Interlock Switch (S51)
A door interlock switch rated 14A at 125VAC is wired in se-
ries with line voltage. When the blower door is removed the
unit will shut down.
FIGURE 2
CONTROL BOX
G40UH(X)
SureLight Control
Transformer
DoorInterlock Switch
WARNING
Shock hazard.
Disconnect power before servicing. Control is
not field repairable. If control is inoperable, sim-
ply replace entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.
3. SureLight Ignition Control (A92) Figure 3
Control 56L84, 10M93 & 32M88
The Lennox SureLight ignition system consists of ignition
control board, ignitor and sensor. The board and ignitor
work in combination to ensure furnace ignition and ignitor
durability. The SureLight integrated board controls all ma-
jor furnace operations. The board also features two LED
lights (DS1, DS2) for troubleshooting and two accessory
terminals rated at (1) one amp. Table 1 gives control termi-
nal designations. Tables 2 and 3 show jack plug terminal
designations. See table 11 for troubleshooting diagnostic
codes. Units equipped with the SureLight board can be
used with either electronic or electro−mechanical thermo-
stats without modification. The SureLight ignitor is made
of durable silicon−nitride. Ignitor longevity is also en-
hanced by voltage ramping by the control board. The
board finds the lowest ignitor temperature which will suc-
cessfully light the burner, thus increasing the life of the ig-
nitor.
TABLE 1
PARK
TERMINAL DESIGNATIONS
COOL−H
HEAT−H
EAC−H
HUM−H
XFMR−H
LINE−H
LINE−N
HUM−N
EAC−N
XFMR−N
CIR−N
Blower − Cooling Speed (120VAC)
Blower − Heating Speed (120VAC)
Electronic Air Cleaner (120VAC)
Humidifier (120VAC)
Transformer (120VAC)
Input (120VAC)
Input (Neutral)
Humidifier (Neutral)
Electronic Air Cleaner (Neutral)
Transformer (Neutral)
Blower − Neutral
(FLAME SENSE)
Alternate Blower Speeds (Dead)
Flame Sensor
120V HOT
120V NEUT