Lennox International Inc. G24-200 - Manual (Page 34)

Page 34
12 −If the furnace does not light the first time (the gas line
may not be 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 Unit" and call your service techni-
cian or gas supplier.
B − Turning Off Gas To Unit
1 − Set the thermostat to the lowest setting.
2 − Turn off all electrical power to the unit if service is to be
performed.
3 − Remove the control access panels.
4 − Perform the following to both gas valves − Turn knob on
gas valve 180
_ either way to OFF. Do not force.
5 − Replace the control access panels.
Heating Sequence of Operation
A − Applications with Single-Stage Thermostat
1 − When the thermostat calls for heat, the K13 and K19
relay contacts close (W1 and W2 jumpered on furnace
terminal strip) and both combustion air blowers (B6
and B16) start.
2 − The combustion air pressure switches (S18 and S45)
prove blower operation, then ignition controls (A3 and
A12) are energized. The pressure switches are factory
set and require no adjustment.
3 − After a pre-purge of 30 seconds, the two spark ignitors
energize and the gas valves (GV1 and GV3) open on
low heat and after approximately 3 seconds open on
high heat.
4 − The sparks ignite the gas, the ignition sensors prove
the flames and the combustion process continues.
5 − In the event that the flames are not detected after the
first trial for ignition (8 seconds trial duration), the igni-
tion controls will repeat steps 3 and 4 two more times
before locking out. (The two ignition controls operate
independently. If one control locks out its gas valve, the
other control maintains its gas valve in operation.)
6 − When W1 heating demand is satisfied, the K13 and
K19 relay contacts open and both gas valves (GV1 and
GV3) close on second-stage after 3 seconds and then
close on first-stage.
7 − For troubleshooting purposes, an ignition attempt after
lockout may be re-established manually. Move thermo-
stat from Heat" to OFF" then back to Heat." The heat-
ing sequence then restarts at step 1.
B − Applications with Two-Stage Thermostat
1 − When the thermostat calls for heat, the K13 relay con-
tacts close (W1 and W2 not jumpered on furnace ter-
minal strip) and both combustion air blowers (B6 and
B16) start.
2 − The combustion air pressure switches (S18 and S45)
prove blower operation, then the ignition controls (A3
and A12) are energized. The pressure switches are
factory set and require no adjustment.
3 − After a pre-purge of 30 seconds, the two spark ignitors
energize and the gas valves (GV1 and GV3) open on
low heat.
4 − The sparks ignite the gas, the ignition sensors prove
the flames and the combustion process continues.
5 − In the event that the flames are not detected after the
first trial for ignition, the ignition controls will repeat
steps 3 and 4 two more times before locking out. (The
two ignition controls operate independently. If one con-
trol locks out its gas valve, the other control maintains
its gas valve in operation.)
6 − If the temperature of the conditioned space continues
to drop, the thermostat’s second-stage contacts close
(W2 powered).
7 − The K19 relay contacts close and the gas valves (GV1
and GV3) open on high heat after approximately 3
seconds.
8 − When the W2 heating demand is satisfied, the K19
relay contacts open and both gas valves (GV1 and
GV3) close second-stage after 3 seconds and then re-
turn to low heat operation. When the W1 heating de-
mand is satisfied, the K13 relay contacts open and
both gas valves (GV1 and GV3) close first-stage.
9 − For troubleshooting purposes,an ignition attempt after
lock-out may be re-established manually. Move the
thermostat from Heat" to OFF" then back to Heat."
The heating sequence then restarts at step 1.