Lennox SLP99UHV Series Unit Information page 21

Electronic Ignition
At the beginning of the heat cycle the SureLight
ed control monitors the low fire combustion air inducer
pressure switch. The control will not begin the heating cy-
cle 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 con-
trol will allow high fire heat. Once the low fire pressure
switch is determined to be open, the combustion air induc-
er 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 begins. If the switch is not proven within 2-1/2 min-
utes, the inducer is de-energized and the control will initi-
ate vent calibration. If the vent calibration is unsuccessful
the control goes into a 5 minute delay. The control will
attempt vent calibration 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 prov-
en 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 vari-
able capacity and two-stage modes are only operational
with a two-stage thermostat. The thermostat selection is
made using 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 con-
trol will vary the firing rate anywhere between 35% and
100% of full capacity. The indoor blower will be automat-
ically adjusted accordingly to provide the appropriate air-
flow 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 increase to 70%. After this initial rate
increase to 70% capacity, 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 satisfied or another call for high
fire is initiated.
Three-Stage Timed Operation
integrat- Using a single-stage thermostat the system will operate
®
in a three stage timed mode. Upon a call for heat and a
successful ignition, the combustion air inducer will operate
at 35% and the indoor blower will adjust to the appropriate
cfm. After a field selectable 7 or 12 minute delay period,
the inducer RPM will increase and the unit will operate at
70%. The indoor blower will adjust to the appropriate cfm.
After a factory 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 op-
erate at 70% and the indoor blower will adjust to the ap-
propriate 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 contin-
uous W2 call) expires the furnace will increase to 100%
rate. The inducer 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.
SureLight® Control 6 Pin Terminal Designation
SureLight Control 12 Pin Terminal Designation
Page 21
TABLE 1
Pin #
1 Data Input From Motor
2
3
4 Data Output To Motor
5 5 Volt Bias Supply
6
TABLE 2
Pin #
1
2 High Fire Pressure Switch
3
4
5
6 Primary Limit In
7
8 Gas Valve Common
9
10
11 Primary Limit Switch Out
12 Low Fire Pressure Switch
Function
Common
Not Used
Not Used
Function
Not used
Rollout In
Ground
24V Hot
Gas Valve
24V Neutral
Ground