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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−Heating Fan Delay Time
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 7 for switch settings and
fan delay times.
e−Cooling Fan Delay Time
The cooling fan on time is fixed at 2 seconds and cannot be
adjusted. G40DF units do not have a cooling fan off delay
time.
TABLE 7
S1 DIP SWITCH SETTINGS
Heat Off Delay
Switch 1
Switch 2
Seconds
OFF
OFF
60
OFF
ON
90
ON
OFF
120
ON
ON
180
5. Ignition Control (A92) Figure 6
Control 78M47 & 100973−01
WARNING
Shock hazard.
Disconnect power before servicing. Control is
not field repairable. If control is inoperable, sim-
ply replace entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.
The hot surface ignition system consist of an integrated
control board (figure 6 with control terminal designations
in table 10), sensor (figure 9) and ignitor (figure 10). The
control board and ignitor work in combination to ensure
furnace ignition and ignitor durability. The control board
controls all major furnace operations. The control board
also features two LED lights (AN1 red and AN2 green) for
troubleshooting and two accessory terminals rated at (1)
one amp. The control board also features a (3) amp fuse for
overcurrent protection. Tables 8 and 9 show jack plug ter-
minal designations. See table 11 for troubleshooting diag-
nostic codes. The mini−nitride ignitor is made from a non−
porous, high strength proprietary ceramic material that
provides long life and trouble free maintenance. The con-
trol board continuously monitors line voltage and main-
tains the ignitor power at a consistent level to provide
proper lighting and maximum ignitor life.