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1 − When there is a call for heat, W1 of the thermostat energizes W of the furnace control with 24VAC.
2 − S10 primary limit switch, S47 rollout switch and S21 secondary limit are closed. Call for heat can continue.
3 − Ignition control (A92) energizes combustion air inducer B6. Combustion air inducer runs until S18 combustion air prove switch closes (switch
must close within 2−1/2 minutes or control goes into 5 minute Watchguard Pressure Switch delay). Once S18 closes, a 15−second pre−purge
follows.
4 − Ignition control (A92) energizes ignitor. A 20−second warm−up period begins.
5 − Gas valve opens for a 4−second trial for ignition
6 − Flame is sensed, gas valve remains open for the heat call.
7 − After 45−second delay, ignition control (A92) energizes indoor blower B3.
8 − When heat demand is satisfied, W1 of the indoor thermostat de−energizes W of the ignition control which de−energizes the gas valve
Combustion air inducer B6 continues a 5−second post−purge period, and indoor blower B3 completes a selected OFF time delay.
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