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I-UNIT COMPONENTS
EL297UHV(X) unit components are shown in FIGURE 1.
The gas valve, combustion air inducer and burners can be
accessed by removing the access panel. Electrical com-
ponents are in the control box (FIGURE 2) found in the
blower section.
EL297UHV(X) units are factory equipped with a bottom
return air panel in place. The panel is designed to be eld
removed as required for bottom air return. Markings are
provided for side return air and may be cut out in the eld.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic discharge can aect electronic
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
secondary.
2. Door Interlock Switch (S51)
A door interlock switch rated 14A at 125VAC is wired in se-
ries with line voltage. When the inner blower access panel
is removed the unit will shut down.
CONTROL BOX
Door Interlock Switch
Circuit Breaker
Blower Drive
(some units)
Tw-Stage Variable Speed
Ignition Control
Transformer
FIGURE 2
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 shutdown. The breaker can be manually
reset by pressing the button on the face. See FIGURE 3.
PRESS TO RESET
FIGURE 3
WARNING
Shock hazard.
Disconnect power before servicing. Integrated control
is not eld repairable. If control is inoperable, simply
replace entire control.
Can cause injury or death. Unsafe operation will result if
repair is attempted.
4. Blower Drive (See Indoor Blower Section)
5. Integrated Control (A92)
Units are equipped with a communicating enabled Sure-
Light
®
two-stage, variable speed integrated control. This
control is used with a communicating thermostat as part
of a communicating comfort system. The control can also
operate with a non-communicating conventional single or
two-stage thermostat. The system consists of a ignition
/ blower control (FIGURE 4 and FIGURE 6) with control
pin designations in TABLE 1, TABLE 2 and TABLE 3 and
ignitor (FIGURE 15). The control and ignitor work in com-
bination to ensure furnace ignition and ignitor durability.
The control provides gas ignition, safety checks and in-
door blower control with two-stage gas heating.
The furnace 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 ame signal. The control features a seven-segment
LED display, indicating furnace status (including indoor
blower) and error codes. The LED ashes in single digits.
The control also has two unpowered (dry) 1/4” contacts for
a humidier 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 rst stage and second stage combustion air
inducer prove switch. The control will not begin the heating
cycle if the rst stage prove switch is closed (by-passed).
Likewise the integrated control will not begin the second
stage heating cycle if the second stage prove switch is
closed, and will remain in rst stage heat. However, if the
second stage prove switch closes during the rst stage
heat pre-purge, the control will allow second stage heat.
Once the rst stage prove switch is determined to be
open, the combustion air inducer is energized on low (rst
stage) heat speed.
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