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I-UNIT COMPONENTS
SLP99UHV 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 blow-
er compartment. SLP99UHV units are factory-equipped
with a bottom return air panel in place. The panel is de-
signed to be field removed as required for bottom air re
-
turn. Markings are provided for side return air and may be
cut out in the field.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic discharge can affect
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. Interlock Switch (S51)
An interlock switch rated 14A at 125VAC is wired in series
with line voltage. When the inner blower access panel is
removed the unit will shut down.
CONTROL BOX
SURELIGHT®
INTEGRATED
CONTROL
TRANSFORMER
CIRCUIT
BREAKER
INTERLOCK
SWITCH
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 shut
down. 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 field
repairable. If control is inoperable, simply
replace entire control. Can cause injury
or death. Unsafe operation will resul if
repair is attempted.
4. Integrated Control (A92)
SLP99UHV units are equipped with the Lennox SureLight
®
variable-capacity integrated control. This control can be
used with the icomfort Wi-Fi
®
thermostat as part of a com-
municating comfort system. The control can also operate
with a conventional single or two-stage thermostat. The
system consists of an ignition / blower control (FIGURE 4
and FIGURE 5) with control pin designations in TABLE 1
and TABLE 2, and ignitor.
The control provides gas ignition, safety checks and in-
door blower control with variable capacity rate gas heat-
ing. The furnace combustion air inducer, gas valve and in-
door 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-seg
-
ment LED display, indicating furnace status (including in-
door blower) and error codes. The LED flashes in single
digits. For example using table 14 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 120 volt
accessory terminals (used for a humidifier and electronic
air cleaner) rated at (1) one amp each.
