I Unit Components - Lennox EL280UH110P60C Unit Information

I−UNIT COMPONENTS
EL280UH(X) unit components are shown in figure 1. The
gas valve, combustion air inducer and burners can be ac-
cessed by removing the access panel. Electrical compo-
nents are in the control box (figure 2) found in the blower
section.
EL280UH(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.
CAUTION
Electrostatic discharge can affect elec-
tronic components. Take precautions to
neutralize
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)
A door interlock switch is wired in series with line voltage.
When the inner blower access panel is removed the unit
will shut down.
CONTROL BOX EL280UH
Transformer
Circuit Breaker
FIGURE 2
electrostatic charge
Interlock Switch
®
SureLight Integrated Control
3. Circuit Breaker (CB8)
A 24V circuit breaker is also located in the control box.
The switch provides overcurrent protection to the trans-
former (T1). The breaker is rated 3A at 32V. If the current
exceeds this limit the breaker will trip and all unit opera-
tion will shutdown. The breaker can be manually reset
by pressing the button on the face. See figure 3.
CIRCUIT BREAKER CB8
PRESS TO RESET
Shock hazard.
by
Disconnect power before servicing. Integrated
control is not field repairable. If control is inoper-
able, simply replace entire control.
Can cause injury or death. Unsafe operation will re-
sult if repair is attempted.
4. Integrated Control (A92)
EL280UH units are equipped with the Lennox two−stage
integrated SureLight
ignition / blower control (figures 5 and 6) with control pin
designations 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.
Page 8
FIGURE 3
WARNING
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control. The system consists of a