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27
SEQUENCE OF OPERATION FLOW CHART
Thermostat calls for heat
Switch power on to unit
VFD sends power to Blower
Blower engages Prover Switch
Blower runs at low speed
After 30 seconds, Ignition
Control provides power to
Spark Igniter and opens Gas
Valve
Ignition Control maintains spark for up
to 4 seconds and monitors Flame
Sensor to determine if Burner is lit
Does Burner
light?
Ignition Control changes Blower from
low speed to high speed after 5 seconds
Ignition Control monitors
flame signal
Thermostat is satisfied
Blower – off; Blower Prover – opens
Ignition Control – off; Gas Valve – closes
Wait 15 minutes.
Blower runs at
low speed
Is this the third loss
of flame signal?
Is this the third
ignition trial?
Loss of flame signal?
YES
YES
NO
NO
GasValve –off
GasValve –off
NO
NO
YES
YES
FIGURE 24.