Lennox International Inc. o23v - Manual (Page 23)

Page 23
VIII−WIRING DIAGRAMS AND SEQUENCE OF OPERATIONS
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1. When disconnect is closed, 120V is routed to control
board (A15). The control board feeds line voltage to trans-
former (T1).
2. When there is a call for heat, W1 of the thermostat ener-
gizes W of the A15 board with 24VAC.
3. A15 energizes combustion air inducer B6 (burner motor)
assuming primary limit (S10) is closed.
4. Burner control A3 energizes the electronic ignitor caus-
ing a 20,000VAC spark . Pump valve (L35) is delayed
for a 15 second pre−purge. The pre−purge is followed by
a 15 second trial for ignition.
5. After the pre−purge and trial for ignition (30 seconds)
voltage passes through contactor K1 the energizing the
indoor blower B3 on heating speed.
6. When heat demand is satisfied, W1 of the thermostat
de-energizes W of the ignition control. Combustion air
inducer B6 is de−energized. The indoor blower ramps
down to 82% for 3 1/2 minutes then shuts off.
7. When there is a call for cooling, Y1 of the thermostat ener-
gizes Y and G of the A15 board with 24VAC.
8. A15 energizes relay K2. When K2 contacts close, the in-
door blower B3 energizes on cooling speed.
9. When cooling demand is satisfied, Y1 of the thermostat
de-energizes Y and G. The condensing unit shuts off im-
mediately and the indoor blower ramps down to 82% for
60 seconds then shuts off.