Lennox EL280UHE Series Unit Information page 8

I-UNIT COMPONENTS
EL280UHE(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.
EL280UHE(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 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)
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 EL280UHE(X)
Transformer
Circuit Breaker
FIGURE 2
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.
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)
Units are equipped with the SureLight
grated control. The system consists of a ignition / blower
control (figures 4 and 5) with control pin designations in
tables 1 and 2 and ignitor. The control and ignitor work in
combination to ensure furnace ignition and ignitor durabil­
ity. The control provides gas ignition, safety checks and in­
door blower control with two-stage gas heating. The fur­
nace combustion air inducer, gas valve and indoor blower
are controlled in response to various system inputs such as
thermostat signal, pressure and limit switch signal and
flame signal. The control features a seven-segment LED
display, indicating furnace status and error codes. The LED
flashes in single digits. For example using table 4 under
LIMIT CODE, an "E" followed by "2" followed by "5" fol­
lowed by "0", the limit switch circuit is open. The control also
has two unpowered (dry) 1/4" contacts for a humidifier and
a 120 volt accessory terminal. Both rated at (1) one amp
each.
Electronic Ignition
At the beginning of the heat cycle the integrated 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 integrated control will not begin the
second stage heating cycle if the second stage pressure
switch is closed, and will remain in first stage heat. Howev­
er, 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 deter­
mined 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.
Page 8
FIGURE 3
WARNING
®
two-stage, inte­