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Troubleshooting: Heating Sequence of Operation (Continued)
CALL FOR HEAT SATISFIED
1st Stage Heat
2nd Stage Heat
2nd Stage
Call for Heat
satisfied?
NO
1st Stage
Call for Heat
satisfied?
Gas valve
De−Energized
YES
NO
1 4
3A 3B
YES
OR
Combustion Air Inducer
switched to 70% rate speed
Adjust Indoor Blower
to appropiate speed
Combustion Air Inducer OFF
after 20−Second Post Purge
Indoor Blower OFF
after OFF Delay
RUN MODE (SINGLE−STAGE THERMOSTAT)
ALL INPUTS MONITORED (LIMIT, PRESSURE,
CALL FOR HEAT/COOL, FLAME LEVEL).
RUN MODE (TWO−STAGE THERMOSTAT)
FIRST OR SECOND−STAGE CALL FOR HEAT
ALL INPUTS MONITORED (LIMIT, PRESSURE,
CALL FOR HEAT/COOL, FLAME LEVEL).
Wait for Call
Two−Stage
Thermostat
Wait for Call
Single−Stage
Thermostat