Sequence Of Operation - LG AR-DR12-05A Installation And Operation Manual

INDIRECT GAS FIRED FURNACES

Sequence of Operation

Start-Up / Standby
Prior to start-up, verify that all field-installed sensors have been installed. This includes a room temperature sensor (optional) and a dis-
charge air temperature sensor (standard).
Heat Mode
When the unit or furnace controller calls for heat:
1. The ignition control will check that the pressure switch for the combustion blower is open.
2. The combustion blower will energize and the 15 second pre-purge begins.
3. The gas valve is energized and the igniter will spark for up to 10 seconds. If a flame is not sensed during the trial for ignition, two addition-
al tries will be attempted before going into lockout for one hour.
4. When a flame is sensed, sparking stops immediately. The gas valve and combustion blower remain energized.
5. Ignition
4:1 Electronic Modulation: The burner will light at 100% fire and remain there for 10 seconds. The main burner gas valve will then
modulate from 100% down to a minimum of 25%, as needed. The combustion blower will change between high and low speed to maintain
acceptable combustion airflow. If the high speed pressure switch does not pull in when required, the furnace will lock out.
High Turndown Electronic Modulation: The furnace controller will ignite the necessary manifold(s) at 100% for 10 seconds. The main
burner gas valves will then modulate from 100% down to a minimum of 25% as needed. The combustion blower will change between
high and low speed to maintain acceptable combustion airflow. If less heat is needed, a manifold section will be turned off. Each time a
manifold section is initialized, the manifold section will ignite at 100%.
6. The ignition control constantly monitors the call for heat, the pressure switch and the burner flame to assure proper operation.
7. When the unit or furnace controls are satisfied, the main gas valve is then de-energized and the combustion blower shuts off following a
30 second post-purge period.
Recovery from Lockout
If the furnace goes into lockout, the ignition control will automatically reset after one hour if the thermostat is still calling for heat. If needed, a
manual reset can be accomplished by either shutting off the power or turning off the call for heat (turn off the thermostat) for a period of five
seconds.
82
Due to our policy of continuous product innovation, some specifications may change without notification.
©LG Electronics U.S.A., Inc., Englewood Cliffs, NJ. All rights reserved. "LG" is a registered trademark of LG Corp.