Lennox EL280UHX Series Unit Information page 9

When the differential in the pressure switch is great
enough, the pressure switch closes and a 15-second pre-
purge begins .
After the 15-second pre-purge period, the SureLight
nitor warms up for 20 seconds after which the gas valve
opens for a 4-second trial for ignition. The ignitor remains
energized 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.
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 speed. After the low & high pressure switch
close, the unit will proceed with a 15 sec pre-purge, fol-
lowed by a 20 sec ignitor warm up, then ignition on high-
fire. After 10 to 20 seconds of high fire operation the unit
will switch to low fire.
Two Stage Operation / Thermostat Selection DIP
Switch
The control can be utilized in two modes: SINGLE-STAGE
thermostat or TWO-STAGE thermostat. The thermo-
stat selection is made using a DIP switch and must be
positioned 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 "recog-
nition period". DIP switch 2, labeled 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 second-stage heat. While in the
two-stage thermostat mode, 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 on first stage heat
and switch to second stage heat after 30 seconds of oper-
ation. See Sequence of Operation flow charts in the back
of this manual for more detail.
SureLight
Pin #
ig-
®
1
2
3
4
5
SureLight
®
Pin #
1
2
3
4
5
6
7
8
9
10
11
12
Page 9
TABLE 1
Control 5 Pin Terminal Designation
®
Function
Ignitor
Combustion Air Inducer High Speed
Combustion Air Inducer Low Speed
Combustion Air Inducer Neutral
Ignitor Neutral
TABLE 2
Control 12 Pin Terminal Designation
Function
Gas Valve Second Stage
Pressure Switch Second Stage
Rolout Switch
Ground
24V Hot
Primary Limit In
Gas Valve First Stage
Gas Valve Common
24V Neutral
Ground
Primary Limit Out
Pressure Switch First Stage