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VII−WIRING DIAGRAM AND SEQUENCE OF OPERATION
1 − When there is a call for heat, W1 of the thermostat en-
ergizes 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 − 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 prove switch
delay). Once S18 closes, a 15−second pre−purge fol-
lows.
4 − 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, control (A92) energizes indoor
blower B3.
8 − When heat demand is satisfied, W1 of the indoor ther-
mostat de−energizes W of the control which de−ener-
gizes the gas valve. Combustion air inducer B6 contin-
ues a 5−second post−purge period, and indoor blower
B3 completes a selected OFF time delay.
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