Page 5
I-UNIT COMPONENTS
Unit components are shown in figure 1. The gas valve,
combustion air inducer and burners can be accessed by re
moving the access panel. Electrical components are in the
control box (figure 2) found in the blower section.
CAUTION
Electrostatic discharge can affect elec
tronic components. Take precautions
to neutralize electrostatic charge by
touching your hand and tools to metal
prior to handling the control.
A- Control Box
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)
An interlock switch rated 14A at 125VAC is wired in series
with line voltage. When the indoor blower access panel is
removed the unit will shut down.
FIGURE 2
CONTROL BOX EL280DF
SureLight
®
Integrated
Control
Interlock
Switch
Transformer
Circuit Breaker
3. Circuit Breaker (CB8)
A 24V circuit breaker is also located in the control box. The
switch provides overcurrent protection to the transformer
(T1). The breaker is rated 3A at 32V. If the current exceeds
this limit the breaker will trip and all unit operation will shut
down. The breaker can be manually reset by pressing the
button on the face. See figure 3.
FIGURE 3
CIRCUIT BREAKER CB8
PRESS TO RESET
WARNING
Shock hazard.
Disconnect power before servicing. Integrated
control is not field repairable.
If control is inoperable, simply replace entire con
trol.
Can cause injury or death. Unsafe operation will
result if repair is attempted.
4. SureLight Integrated Control (A92)
EL280DF units are equipped with the Lennox two-stage in
tegrated SureLight
®
control. The system consists of a igni
tion / blower control (figures 5 and 6) with control pin desig
nations in tables 2 and 3 and and ignitor. The control and
ignitor work in combination to ensure furnace ignition and
ignitor durability. The SureLight integrated control, controls
all major furnace operations. The control features a red
LED light, for furnace status and troubleshooting. The LED
flashes in “X” + “Y” codes. For example using table 4 under
“PRESSURE SWITCH CODES”, if the red LED flashes 2
times, then off for 2 seconds then flashes 3 times, the low
pressure switch is failed open. The control also has two 120
volt accessory terminals rated at (1) one amp each and one
24 volt accessory terminal rated at 0.5 an amp.
Electronic Ignition
At the beginning of the heat cycle the SureLight control
monitors the first stage and second stage combustion air
inducer pressure switch. The control will not begin the
heating cycle if the first stage pressure switch is closed (by-
passed). Likewise the control will not begin the second
stage heating cycle if the second stage pressure switch is
closed, and will remain in first stage heat. However, if the
second stage pressure switch closes during the first stage
heat pre-purge, the control will allow second stage heat.
Once the first stage pressure switch is determined to be
open, the combustion air inducer is energized on low (first
stage) heat speed. When the differential in the pressure
switch is great enough, the pressure switch closes and a
15-second pre-purge begins. If the switch is not proven
within 2-1/2 minutes, the control goes into Watchguard-
Pressure Switch mode for a 5-minute re-set period.
