Lennox SL280UHVX Series Unit Information page 6

Electronic Ignition
At the beginning of the heat cycle the SureLight
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 control will not begin the second stage heating
cycle if the second stage prove switch is closed, and will re-
main in first stage heat. However, if the second stage prove
switch closes during the first stage heat pre−purge, the con-
trol will allow second stage heat. Once the first stage prove
switch is determined to be open, the combustion air induc-
er is energized on low (first stage) heat speed. When the
differential in the prove switch is great enough, the prove
switch closes and a 15−second pre−purge begins.
NOTE − During abnormal conditions such as low supply
voltage or low outdoor temperatures and the low fire pres-
sure switch does not close, the combustion air inducer will
switch to high fire. After a 15 second pre−purge the high fire
pressure switch will close and the unit will begin operation
on high fire. After 20 seconds of high fire operation the unit
will switch to low fire
TABLE 1
SureLight Control 5 Pin Terminal Designation
PIN #
1
2 Combustion Air Inducer High Speed
3 Combustion Air Inducer Low Speed
4
5
TABLE 2
SureLight Control 12Pin Terminal Designation
PIN #
1
2
3
4
5
6
7
8
9
10
11
12
®
control
Function
Ignitor
Combustion Air Inducer Neutral
Ignitor Neutral
Function
Gas Valve High Fire
Second Stage Prove Switch
Rollout In
Ground
24V Hot
Primary Limit In
Gas Valve Low Stage
Gas Valve Common
24V Neutral
Ground
Rollout Switch Out
1st Stage Prove Switch
After the 15−second pre−purge period, the SureLight ignitor
warms up for 20 seconds after which the gas valve opens
for a 4−second trial for ignition. The ignitor energizes during
the trial until flame is sensed. If ignition is not proved during
the 4−second period, the control will try four more times with
an inter purge and warm−up time between trials of 35 sec-
onds. After a total of five trials for ignition (including the ini-
tial trial), the control goes into Watchguard−Flame Failure
mode. After a 60−minute reset period, the control will begin
the ignition sequence again.
Two Stage Operation / Thermostat Selection DIP
Switch
The control can be utilized in two modes: SINGLE−STAGE
thermostat or TWO−STAGE thermostat. The thermostat
selection is made using a DIP switch (figure 5) and must be
positioned for the particular application. DIP switch 1, la-
beled T"STAT HEAT STAGE is factory−set in the OFF posi-
tion for use with a two−stage thermostat. Move the DIP
switch to ON for use with a single stage thermostat.
While in the single−stage thermostat mode (single DIP
switch setting), the burners will always fire on first−stage
heat. The combustion air inducer will operate on low speed
and indoor blower will operate on low heat speed. After a
factory default 10 minute recognition period, the unit will
switch to second stage heat. While in the two−stage ther-
mostat mode (two DIP switch setting) the burners will fire
on first−stage heat. The combustion air inducer will operate
on low speed and indoor blower will operate on low heat
speed. The unit will switch to second−stage heat on call
from the indoor thermostat. If there is a simultaneous call
for first and second stage heat, the unit will fire an first stage
heat and switch to second stage heat after 30 seconds of
operation. See Sequence of Operation flow charts in the
back of this manual for more detail.
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