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I-UNIT COMPONENTS
SL297UHNV 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.
SL297UHNV 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 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.
FIGURE 2
CONTROL BOX SL297UHNV
Transformer
SureLight
®
Integrated Control
Interlock Switch
Circuit Breaker
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 iComfort
®
enabled Sur
eLight
®
two-stage, variable speed integrated control. This
control is used with the iComfort Wi-Fi
®
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 (figures 4 and 5) with control pin designa
tions in tables 1, 2 and 3 and ignitor. The control and ignitor
work in combination to ensure furnace ignition and ignitor
durability. The control provides gas ignition, safety checks
and indoor blower control with two-stage gas heating. The
furnace combustion air inducer, gas valve and indoor blow
er 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 (including indoor blower)
and error codes. The LED flashes in single digits. For ex
ample using table 5 under LIMIT CODE, an “E” followed by
“2” followed by “5” followed by “0”, the limit switch circuit is
open. The control also has two unpowered (dry) 1/4” con
tacts 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 prove switch. The control will not begin the heating
cycle if the first 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 first stage heat. However, if the
second stage prove switch closes during the first stage
heat pre-purge, the control will allow second stage heat.
Once the first stage prove switch is determined to be open,
