Vii-Wiring And Sequence Of Operation - Lennox ML193DFE Series Unit Information

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 and S47 rollout switch are
closed. Call for heat can continue.
3 - The integrated 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 - The integrated 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 30-second delay, the integrated control (A92)
energizes indoor blower B3.
8 - When heat demand is satisfied, W1 of the indoor
thermostat de-energizes W of the integrated 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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