Portal 80_Sequence_of_Operation

1. Each time the thermostat “W” (Heating) contacts close (legacy) or a communicating heat call is transmitted to the furnace control from a communicating thermostat, the furnace control checks to make sure that both pressure switches are open. This is true of a low or high heat call as “W” is energized on either call. Next the induced draft blower (inducer) begins a pre-purge cycle at high stage.

2. The air proving negative pressure switches (both low and high) close. Inducer will then immediately shift to low speed.

3. After the 30-second pre-purge, the gas valve opens on low stage for an 8-second trial for ignition.

4. The spark igniter is energized to light the gas burners and stays energized for the up to 7 seconds after the gas valve opens.

5. Eight seconds after the gas valve opens the remote flame sensor must prove flame ignition for one second using the process of flame rectification. If the burners don’t light, the system goes through another ignition sequence. It does this up to four times before entering a 1-hour lockout.

6. Twenty seconds after flame is sensed, the gas valve is set to the thermostat demand (low or high) and the main blower will be energized at either the low or high gas heat stage depending on the thermostat demand.

7. When the thermostat “W” (legacy) or communicated heat call ends, the gas valve closes, flame is extinguished, the induced draft blower stops after a 10-second post-purge, and the negative pressure switch opens.

8. The main blower continues until timed off by the setting on the integrated furnace control board.