Electrostatic Discharge (Esd); Electronic Ignition; Fan Time Control; Fan-Off Time Adjustment - Lennox G24M SERIES Unit Information

TABLE 3
SureLight BOARD J156 (J2) TERMINAL
DESIGNATIONS
PIN #
1
2
3
4 Combustion Air Blower Line Voltage
5
6 Combustion Air Blower Neutral
TABLE 4
SureLight BOARD J58 (J1) TERMINAL
DESIGNATIONS
PIN #
1
2
3
4
5
6 Pressure Switch and Primary Limit Out
7
8
9

ELECTROSTATIC DISCHARGE (ESD)

Precautions and Procedures
CAUTION
Electrostatic discharge can affect electronic
components. Take precautions during furnace
installation and service to protect the furnace's
electronic controls. Precautions will help to
avoid control exposure to electrostatic dis-
charge by putting the furnace, the control and
the technician at the same electrostatic poten-
tial. Neutralize electrostatic charge by touching
hand and all tools on an unpainted unit surface,
such as the gas valve or blower deck, before per-
forming any service procedure.
b-Electronic Ignition
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 prove 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
FUNCTION
Ignitor
Not Used
Ignitor Neutral
Not Used
FUNCTION
Primary Limit In
Gas Valve Common
Roll Out Switch Out
Gas Valve 24V
Pressure Switch In
Not Used
Roll Out Switch In
Ground
not proven within 2-1/2 minutes, the control goes into
Watchguard-Pressure Switch mode for a 5-minute re-set
period.
NOTE - The G24M furnace contains electronic com-
ponents that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.
After the 15-second pre-purge period, the SureLight igni-
tor warms up for 20 seconds after which the gas valve
opens for a 4-second trial for ignition. The ignitor stays en-
ergized for the first second of the 4-second trial. G24M
units with 63K89, 24L85 or 56L83: the ignitor stays ener-
gized the first second of the 4 second trial. G24M units with
board 97L48: ignitor stays energized during the 4-second
trial until flame is sensed. If ignition 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 sec-
onds. After a total of five trials for ignition (including the ini-
tial 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
prolongs the life of the ignitor. After a successful ignition,
the SureLight control utilizes less power to energize the ig-
nitor 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 low-
est power is determined and the cycle begins again.
c-Fan Time Control
The 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 flipping the dip
switches located on the SureLight integrated control. 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. See figure 8.
NOTE—If fan "off" time is set too low, residual heat in
heat exchanger may cause primary limit S10 to trip re-
sulting in frequent cycling of blower. If this occurs, ad-
just blower to longer time setting.

FAN-OFF TIME ADJUSTMENT

60sec.
To adjust fan-off timing, flip dip switch to desired setting.
Page 10
90sec. 120sec.
FIGURE 8
180sec.