Lennox SL280UHNV - Page 11

Page 11
I-Unit Components
SL280UHNV 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.
SL280UHNV units are factory equipped with a bottom re-
turn 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 a󰀨ect electronic components.
Take precautions during furnace installation and service
to protect the furnace’s electronic controls. Precautions
will help to avoid control exposure to electrostatic
discharge by putting the furnace, the control and the
technician at the same electrostatic potential. Neutralize
electrostatic charge by touching hand and all tools on an
unpainted unit surface, such as the gas valve or blower
deck, before performing any service procedure.
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
Transformer
SureLight
®
Integrated Control
Interlock Switch
Circuit Breaker
FIGURE 2
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
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. 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 5) with control pin des-
ignations in Table 1, Table 2 and Table 3 and ignitor Figure
13. 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
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 dig-
its. For example 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” contacts for a humidier and a 120 volt accesso-
ry 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. When the di󰀨erential in the prove switch is
great enough, the prove switch closes and a 15-second
pre-purge begins.