Wiring And Sequence Of Operation - Lennox G71MPP SERIES Unit Information

VII− Wiring and Sequence of Operation
NOTE − The thermostat selection DIP switch on the control
board is factory−set in the TWO−STAGE" position.
Applications Using a Two−Stage Thermostat
A − Heating Sequence −− Control Board Thermostat
Selection DIP switch in Variable Capacity" Position
1. On a call for heat, thermostat first−stage contacts close
sending a signal to the integrated control. The inte-
grated control runs a self-diagnostic program and
checks high temperature limit switches for normally
closed contacts and pressure switches for normally
open contacts.The combustion air inducer is ener-
gized at ignition speed, which is approximately the
same as the inducer speed at 70 percent firing rate.
2. Once the control receives a signal that the low−fire
pressure switch has closed, the combustion air induc-
er begins a 15−second pre−purge in ignition speed.
3. After the pre−purge is complete, a 20−second initial ig-
nitor warm−up period begins. The combustion air in-
ducer continues to operate at the ignition speed.
4 − After the 20−second warm−up period has ended, the gas
valve is energized and ignition occurs. At the same time,
the control module begins an indoor blower 45−second
ON−delay. When the delay ends, the indoor blower
motor is energized at a speed that matches the firing
rate. After the 10−second ignition stabilization delay
expires, the inducer speed is adjusted to the appropri-
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