Page 15
Electronic Ignition
At the beginning of the heat cycle the SureLight
®
integrated
control monitors the low fire combustion air inducer pres-
sure switch. The control will not begin the heating cycle if the
low fire pressure switch is closed (by−passed). Likewise the
control will not begin the high fire heating cycle if the high fire
pressure switch is closed, and will remain in low fire heat.
However, if the high fire pressure switch closes during the
low fire heat pre−purge, the control will allow high fire heat.
Once the low fire pressure switch is determined to be open,
the combustion air inducer is energized on ignition speed.
When the differential in the pressure switch is great enough,
the pressure switch closes and a 15−second pre−purge be-
gins. If the switch is not proven within 2−1/2 minutes, the in-
ducer is de−energized and the control will initiate vent cal-
ibration. If the vent calibration is unsuccessful the control
goes into a 5 minute delay. The control will attempt vent cal-
ibration 3 more times before going into a 1 hour soft lockout.
After the 15 second pre−purge period the SureLight ignitor
warms up for 20 seconds. The gas valve then opens for a
4−second trial for ignition. The ignitor stays energized during
this trial until flame is sensed. If ignition is not proven during
the 4−second trial for ignition, 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.
Thermostat Selection Modes
See table 3 for DIP switch settings
The control can be made to operate in three modes: vari-
able capacity, three−stage timed or two−stage. The variable
capacity and two−stage modes are only operational with a
two−stage thermostat. The thermostat selection is made us-
ing dip switches one and / or two (figure 4) and must be
positioned for the particular application.
Variable Capacity
Using a two−stage thermostat the system will operate in a
variable capacity sequence mode. In this mode, the control
will vary the firing rate anywhere between 35% and 100% of
full capacity. The indoor blower will be automatically ad-
justed accordingly to provide the appropriate airflow at any
rate. On the initial call for low fire, the furnace will operate at
35% and will remain there until the heat call is satisfied or a
call for high fire is initiated. If there is a call for high fire the
rate will increase
by
10% if the current rate is above 60%.
However, if the current rate is below 60% the rate will in-
crease
to
70%. After this initial rate increase to 70% capac-
ity, the furnace will increase rate by 10% every 5 minutes
while a high fire heat call is present. If the high fire heat call is
satisfied but the low fire heat call is still present, the furnace
will remain at the current firing rate until the demand is satis-
fied or another call for high fire is initiated.
Three−Stage Timed Operation
Using a single−stage thermostat the system will operate in a
three stage timed mode. Upon a call for heat and a success-
ful ignition, the combustion air inducer will operate at 35%
and the indoor blower will adjust to the appropriate cfm. Af-
ter a field selectable 7 or 12 minute delay period, the induc-
er RPM will increase and the unit will operate at 70%. The
indoor blower will adjust to the appropriate cfm. After a fac-
tory set non−adjustable 10 minute delay expires the furnace
will increase rate to 100%. The indoor blower will adjust to
the appropriate cfm.
Two−Stage Operation
The system will also operate in conventional two−stage
mode. While in two−stage mode, the furnace will fire on low
fire (70% rate). The combustion air inducer will operate at
70% and the indoor blower will adjust to the appropriate
cfm. The unit will switch to high fire on a W2 call from the
thermostat. After a 30 second recognition period (during
which the integrated control will receive a continuous W2
call) expires the furnace will increase to 100% rate. The in-
ducer will increase to 100% speed and the indoor blower will
adjust to appropriate cfm. 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
operation.
TABLE 1
SureLight
®
Control 6 Pin Terminal Designation
PIN #
Function
1
Data Input From Motor
2
Common
3
Not Used
4
Data Output To Motor
5
5 Volt Bias Supply
6
Not Used
TABLE 2
SureLight Control 12 Pin Terminal Designation
PIN #
Function
1
Not used
2
High Fire Pressure Switch
3
Rollout In
4
Ground
5
24V Hot
6
Primary Limit In
7
Gas Valve
8
Gas Valve Common
9
24V Neutral
10
Ground
11
Primary Limit Switch Out
12
Low Fire Pressure Switch
