Lennox LGT Series Unit Information page 24

D-GAS HEAT COMPONENTS
1-Control Box Components A3, A55, T3, K13
WARNING
Shock hazard. Spark related components
contain high voltage which can cause
personal injury or death. Disconnect
power before servicing. Control is not
field repairable. Unsafe operation will
result. If control is inoperable, simply
replace the entire control.
Burner Ignition Control A3
The ignition controls are located in the heat section areas
below the compressors. The controls are manufactured
UTEC. See table 6 for LED codes.
The ignition control provides three main functions: gas
valve control, ignition and flame sensing. The unit will
usually ignite on the first attempt; however, the ignition
attempt sequence provides three trials for ignition before
locking out. The lockout time for the control is 5 minutes.
After lockout, the ignition control automatically resets and
provides three more attempts at ignition.
ON / CLOSED
OFF / OPEN
THERMOSTAT DEMAND
COMBUSTION AIR BLOWER
COMBUSTION AIR PROVE SWITCH
IGNITION SPARK
IGNITION TRIAL
ON
OFF
THERMOSTAT DEMAND
COMBUSTION AIR BLOWER
COMBUSTION AIR PROVE SWITCH
IGNITION SPARK
IGNITION TRIAL
NORMAL IGNITION SEQUENCE - TIMINGS NOMINAL
S E C O N D S 0 5
GAS VALVE
BLOWER
RETRIALS - IGNITION ATTEMPT SEQUENCE - TIMINGS NOMINAL
SECONDS 0 5 30 35
GAS VALVE
BLOWER
Manual reset after lockout requires breaking and remak-
ing power to the ignition control. See figure 11 for a normal
ignition sequence and figure 12 for the ignition attempt
sequence with retrials (nominal timings given for simplic-
ity). Specific timings for the ignition controls are shown in
figure 13.
LED Flashes
Slow Flash
Fast Flash
Steady Off
Steady On Failure Control internal failure
1 Flash
2 Flashes
3 Flashes
4 Flashes
5 Flashes
6 Flashes
7 Flashes
8 Flashes
3 0 3 5 70
END OF
DEMAND
1
FIGURE 11
65 70
FIGURE 12
Page 24
TABLE 6
Indicates
Control ok, no call for heat
Control ok, call for heat present.
Internal control fault or no power
Rollout switch open
Limit open or lockout from to many
tries during a single heat demand
Pressure switch open with inducer
on/ open during 5 minute inducer
off time.
Ignition lockout from no flame
detected or from too many flame
losses.
Flame sensed out of sequence
Pressure switch closed with induc-
er off
Gas valve relay failure
Lockout due to too many pressure
switch openings during one heat
demand
0 5
100 105
WATCHGUARD
LOCKOUT
1 1 0