Lennox SL280UHV Series Unit Information page 18

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,
the combustion air inducer 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 op-
eration on high fire. After 10 to 20 seconds of high fire
operation the unit will switch to low fire.
After the 15-second pre-purge period, the SureLight ig-
nitor warms up for 20 seconds after which the gas valve
opens for a 4-second trial for ignition. The ignitor energiz-
es 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 seconds.
After a total of five trials for ignition (including the initial
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 and must be posi-
tioned for the particular application. DIP switch 1, labeled
T"STAT HEAT STAGE is factory-set in the OFF position 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, the burners
will always fire on first-stage heat. The combustion air in-
ducer will operate on low speed and indoor blower will
operate on low heat speed. The unit will switch to second
stage heat after a "recognition period". DIP switch 2, la-
beled SECOND STAGE DELAY, is factory set in the OFF
position for a 7 minute recognition period. The switch can
be moved to the ON position for a 12 minute recognition
period, after which time the unit will switch to secondstage
heat.
While in the two-stage thermostat mode (two DIP switch
setting) the burners will fire on first-stage heat. The com-
bustion 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 Oper-
ation flow charts in the back of this manual for more detail.
SureLight Control 5 Pin Terminal Designation
®
PIN#
1
2
3
4
5
SureLight Control 12 Pin Terminal Designation
®
PIN#
1
2
3
4
5
6
7
8
9
10
11
12
SureLight Control 6 Pin Terminal Designation
®
PIN#
1
2
3
4
5
6
Page 18
TABLE 1
Function
Ignitor
Combustion Air Inducer High
Speed
Combustion Air Inducer Low
Speed
Combustion Air Inducer Neu-
tral
Ignitor Neutral
TABLE 2
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
TABLE 3
Function
Data Input From Motor
Common
Not Used
Data Output To Motor
5 Volt Bias Supply
Not Used