Lennox International Inc G24-200 installation instructions Heating Sequence of Operation

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 to then back to

The heating sequence then restarts at step 1.

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