5
Heating Sequence of Operation
Listed below is the sequences of operation that occurs when there is a call for heat:
• The green LED will be on at all times. It only ashes during a fault.
• Thermostat contacts close board terminals R & W together
• The 24 VAC at terminal W goes through the limit string rst
• Terminal IND sends 115 VAC to the power exhauster
• The air draft causes the pressure switch to close
• After a short delay, 24 VAC powers the gas valve open
• The igniter sparks when the gas valve opens
• Flame is detected when it carries electrical current from the ame rod
• The yellow LED is on, the igniter stops, and the gas valve stays open
• After 30 sec, terminal HEAT sends 115 VAC to power the fan motor
• When satised, thermostat contacts open between R & W
• The gas valve closes. The yellow LED is off. The power exhauster
and fan purge for 60-90 sec, then shut off.
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