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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)
A door interlock switch is wired in series with line voltage.
When the inner blower access panel is removed the unit
will shut down.
FIGURE 2
CONTROL BOX EL280DFE
Transformer
Circuit Breaker
SureLight
®
Integrated
Control
Interlock Switch
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.
FIGURE 3
CIRCUIT BREAKER CB8
PRESS TO RESET
WARNING
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
®
two-stage, inte
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.
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