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Page 36
Heating Sequence of Operation
When there is a call for heat, the integrated control runs a
self check. The control checks for S10 primary limit, S21
secondary limit (s) and S47 rollout switch normally closed
contacts. The control also checks for S102 high heat and
S128 low heat prove switch normally open contacts. Once
self check is complete and all safety switches are opera-
tional, heat call can continue.
Two−Stage Thermostat, Two Stage Heat. Dip Switch
set at TWO".
1− SureLight
®
control energizes combustion air inducer
B6 on low heat speed. Combustion air inducer runs
until S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
NOTE − If the low fire pressure 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 10 to 20
seconds of high fire operation the unit will switch to low fire.
NOTE − If the furnace is operating on continuous fan mode
(terminal R" and G" are energized), the combustion air in-
ducer will energize on high speed, the gas valve will ener-
gize on second−stage heat and the furnace will operate on
high fire. Furnace will stay on high fire for 60 seconds then
switch to low fire.
2− SureLight control begins 20 second ignitor warm up
period.
3− Gas valve opens on first stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
4− Flame is sensed, gas valve remains on first stage heat,
ignitor de−energizes.
5− After 30 second delay, indoor blower B3 is energized
on low heat speed.
The furnace will stay in this mode until first stage de-
mand is satisfied OR a second stage heat demand is
initiated.
6− Second stage heat demand initiated. A 30 second sec-
ond stage recognition period begins.
7− The combustion air inducer ramps up to high heat
speed.
8− S102 high heat prove switch closes and the gas valve
energizes second stage heat.
9− B3 indoor blower switches to high heat speed.
Single−Stage Thermostat, Two Stage Heat. Dip
Switch set at SINGLE"
1− SureLight control energizes combustion air inducer B6
on low heat speed. Combustion air inducer runs until
S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
NOTE − If the low fire pressure 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 10 to 20
seconds of high fire operation the unit will switch to low fire.
NOTE − If the furnace is operating on continuous fan mode
(terminal R" and G" are energized), the combustion air in-
ducer will energize on high speed, the gas valve will ener-
gize on second−stage heat and the furnace will operate on
high fire. Furnace will stay on high fire for 60 seconds then
switch to low fire.
2− SureLight control begins 20 second ignitor warm up
period.
3− Gas valve opens on first stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
4− Flame is sensed, gas valve remains on first stage heat,
ignitor de−energizes.
5− After 30 second delay, indoor blower B3 is energized
on low heat speed.
6− A 10 minute (factory set) or 15 minute (field set) second
stage heat delay period begins.
7− After the delay the combustion air inducer ramps up to
high heat speed.
8− S102 high heat prove switch closes and the gas valve
energizes second stage heat.
9− B3 indoor blower switches to high heat speed.