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LGH/LCH036, 048, 060, 072, 074
5- Move gas valve switch to OFF. See figure 25 or 26.
6- Wait five (5) minutes to clear out any gas. If you then
smell gas, STOP! Immediately call your
gas supplier from a neighbor's phone. Follow the gas
supplier's instructions. If you do not smell gas, go to
the next step.
7- Move gas valve switch to ON. See figure 25 or 26.
8- Close or replace the control access panel.
9- Turn on all electrical power to appliance.
10- Set thermostat to desired setting.
NOTE - When unit is initially started, steps 1 through 9
may need to be repeated to purge air from gas line.
11- The ignition sequence will start.
12- If the furnace does not light the first time (gas line not
fully purged), it will attempt up to two more ignitions
before locking out.
13- If lockout occurs, repeat steps 1 through 10.
14- If the appliance will not operate, follow the
instructions “Turning Off Gas to Appliance” and call
your service technician or gas supplier.
Turning Off Gas to Unit
1- If using an electromechanical thermostat, set to the
lowest setting.
2- Before performing any service, turn off all electrical
power to the appliance.
3- Open or remove the control access panel.
4- Move gas valve switch to OFF.
5- Close or replace the control access panel.
WARNING
Danger of explosion. Can cause injury or
death. Do not attempt to light manually.
Unit has a direct spark ignition system.
Heating Operation and Adjustments
(Gas Units)
A-Heating Sequence of Operation
Single- and Two-Stage
1- On a heating demand the combustion air inducer
starts immediately.
2- Combustion air pressure switch proves inducer
operation. After a 30-second pre-purge, power is
allowed to ignition control. Switch is factory set and
requires no adjustment.
3- Spark ignitor energizes and gas valve solenoid
opens.
4- Spark ignites gas, ignition sensor proves the flame
and combustion continues.
5- If flame is not detected after 8 seconds, the ignition
control will repeat steps 3 and 4 two more times. The
ignition control will wait 5 minutes before the ignition
attempt recycles.
Four-Stage
1- On a heating demand, the combustion air inducer
starts immediately.
2- Combustion air blower (CAB) prove switch allows
inducer operation. Power is then supplied to the A3
ignition control, enabling 1
st
-stage gas heat. The
CAB prove switch is factory-set and requires no
adjustment.
3- After a 30-second pre-purge, the A3 spark ignitor
energizes and gas valve 1 (GV1) solenoid opens.
4- Spark ignites gas on the first two burners, flame
sensor 1 (FS1) proves the flame, and combustion
continues. Timing circuits energize 1
st-
stage, low fire,
for approximately 10 minutes.
5- If flame is not detected after 8 seconds, the ignition
control will repeat steps 3 and 4 two more times. The
ignition control will wait 5 minutes before the ignition
attempt recycles.
6- Before the 10-minute delay applied to 1
st
stage
expires, the timing circuits enable A12 ignition
control.
7- After a 30-second pre-purge, the A12 spark ignitor
energizes and gas valve 3 (GV3) solenoid opens.
8- Spark ignites gas on the remaining five burners,
flame senor 2 (FS2) proves the flame, and
combustion continues. Timing circuits de-activate
1
st-
stage after approximately 10 minutes. The
remaining 5 burners are energized in 2
nd
-stage,
low fire.
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