Control Transformer; Door Interlock Switch; Surelight Integrated Ignition Control; I Unit Components - Lennox G40UH(X) Unit Information

I−UNIT COMPONENTS
G40UH(X) unit components are shown in figures 1, 2, 3
and 4. The gas valve, combustion air inducer and burners
can be accessed by removing the burner access panel.
Electrical components are in the control box (figure 4)
found in the blower section.
G40UH(X) units are factory equipped with a bottom return air
panel in place. The panel is designed to be field removed as
required for bottom air return. Markings are provided for side
return air and may be cut out in the field.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
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.
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.
CONTROL BOX
G40UH(X)
Transformer
SureLight Control
FIGURE 4
DoorInterlock Switch
Page 16
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 Integrated Ignition Control

(A92) 10M93 & 56L84
The Lennox SureLight ignition system consists of ignition
control (figure 5 with control terminal designations in table
1), sensor (figure 10) and ignitor (figure 11). The ignition
control and ignitor work in combination to ensure furnace
ignition and ignitor durability. The ignition control, controls
all major furnace operations. The ignition control also fea-
tures two LED lights for troubleshooting and two accesso-
ry terminals rated at (1) one amp. Tables 2 and 3 show jack
plug terminal designations. See table 4 for troubleshooting
diagnostic codes. Units equipped with the SureLight sys-
tem can be used with either electronic or electro−mechani-
cal thermostats without modification. The SureLight igni-
tor is made of durable silicon−nitride. Ignitor longevity is
also enhanced by voltage ramping by the ignition control .
The ignition control finds the lowest ignitor temperature
which will successfully light the burner, thus increasing
the life of the ignitor.
TABLE 1
SURELIGHT CONTROL TERMINAL DESIGNATIONS
COOL Blower − Cooling Speed (120V)
HEAT Blower − Heating Speed (120V)
PARK Unused Blower Lead (not energized)
FAN Continuous Low Blower Speed
EAC Accessory Terminal (120V)
XFMR
LINE
HUM Heat Only Accessory (120V)
5 Terminals
FS
TABLE 2
SURELIGHT CONTROL J156 (J2) TERMINAL
DESIGNATIONS
PIN #
1 Combustion Air Inducer Line
2
3 Combustion Air Inducer Neutral
4
Transformer (120V)
Input (120V)
120V Neutral
Flamer Sensor
FUNCTION
Ignitor Line
Ignitor Neutral