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I−UNIT COMPONENTS
G41UF unit components are shown in figure 1. The com
bustion air inducer, gas valve and burners can be accessed
by removing the burner access panel. The blower and con
trol box can be accessed by removing the blower access
door. G41UF units are designed for bottom and side re
turn air.
A−MakeUp Box (Figure 2)
A field makeup box is provided for line voltage wiring. Line
voltage wiring to unit is routed from the make up box. The
hot" wire is connected to the door switch and then from the
switch to the SureLight board. The make−up box may be
installed inside or outside the unit and on the unit left or right
side (right side shown figure 2).
FIGURE 2
INTERIOR MAKE−UP BOX INSTALLATION
MAKE−UP
BOX
Right Side
CLAMP LOCATION
B−Control Box Components (Figure 3)
Unit transformer (T1) and SureLight control (A92) are lo
cated in the control box. In addition, a door interlock switch
(S51) is located in the control box.
FIGURE 3
DOOR INTERLOCK
SWITCH (S51)
SURELIGHT
CONTROL
BOARD
(A92)
TRANSFORMER
(T1)
1. Control Transformer (T1)
A transformer located in the control box provides power to
the low voltage 24 volt section of the unit. Transformers on
all models are rated 40VA with a 120V primary and a 24V
secondary.
2. Door Interlock Switch (S51)
A door interlock switch rated 14A at 120VAC is located on
the control box. The switch is wired in series with line volt
age. When the blower door is removed the unit will shut
down.
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. Furnace Control (A92)
All G41UF model units are equipped with the Lennox Sur
eLight ignition system. The system consists of ignition
control board (figure 5 with control terminal designations
in table 3), ignitor (figure 6) and sensor (figure 7). 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 terminals rated at (1) one amp. Tables 1 and 2
show jack plug terminal designations. See table 4 for trou
bleshooting diagnostic codes. The SureLight 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 temperature which will suc
cessfully light the burner, thus increasing the life of the ig
nitor.
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 discharge by
putting the furnace, the control and the techni
cian at the same electrostatic potential. Neutral
ize electrostatic charge by touching hand and all
tools on an unpainted unit surface, such as the
gas valve or blower deck, before performing any
service procedure.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures