Lennox G50UHi Unit Information page 12

c−Electronic Ignition (See Figure 8)
On a call for heat the SureLight control monitors the com-
bustion air inducer prove switch. The control will not begin
the heating cycle if the prove switch is closed (by−passed).
Once the proving switch is determined to be open, the com-
bustion air inducer is energized. When the differential in the
prove switch is great enough, the prove switch closes and a
15−second pre−purge begins. If the prove switch is not
proven within 2−1/2 minutes, the control goes into Watch-
guard−Pressure Switch mode for a 5−minute re−set period.
After the 15−second pre−purge period, the SureLight ignitor
warms up for 20 seconds during which the gas valve opens
at 19 seconds for a 4−second trial for ignition. The ignitor
stays energized during the trial until flame is sensed. If igni-
tion 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.
The SureLight control board has an added feature that pro-
longs the life of the ignitor. After a successful ignition, the
SureLight control utilizes less power to energize the ignitor
on successive calls for heat. The control continues to ramp
down the voltage to the ignitor until it finds the lowest
amount of power that will provide a successful ignition. This
amount of power is used for 255 cycles. On the 256th call
for heat, the control will again ramp down until the lowest
power is determined and the cycle begins again.
d−Fan Time Control Heating
The heating fan on time of 45 seconds is not adjustable.
Fan off time (time that the blower operates after the heat
demand has been satisfied) can be adjusted by setting the
S1 dip switches located on the SureLight integrated con-
trol. The unit is shipped with a factory fan off setting of 90
seconds. Fan off time will affect comfort and is adjustable
to satisfy individual applications. For customized comfort,
monitor the supply air temperature once the heat demand
is satisfied. Note the supply air temperature at the instant
the blower is de−energized. Adjust the fan−off delay to
achieve a supply air temperature between 90° − 110° at the
instant the blower is de−energized. (Longer delay times al-
low for lower air temperature, shorter delay times allow for
higher air temperature). See table 8 for switch settings and
fan delay times..
e−Fan Time Control Cooling
The cooling fan on time is fixed at 2 seconds and cannot be
adjusted. Fan off time (time that the blower operates after
the cool demand has been satisfied) can be adjusted by
setting the S1 dip switches (switch 3) located on the Sur-
eLight integrated control. See table 8 for switch settings
and fan delay times.
S1 DIP SWITCH SETTINGS
Switch 1
OFF
OFF
ON
ON
Cool Off Delay
Switch 3
OFF
ON
Page 12
TABLE 8
Heat Off Delay
Switch 2 SECONDS
OFF
ON
OFF 120
ON 180
SECONDS
60
90
2
45