Page 23
VII− Wiring and Sequence of Operation
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 secon-
dary limit are closed. Call for heat can continue.
3 −
SureLight 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 −
SureLight 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, SureLight control (A92) energizes in-
door blower B3.
8 −
When heat demand is satisfied, W1 of the indoor thermostat
de−energizes W of the SureLight control which de−energizes
the gas valve. Combustion air inducer B6 continues a 5−sec-
ond post−purge period, and indoor blower B3 completes a
selected OFF time delay.
