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VII- Wiring and Sequence of Operation
80UHG-1 MODEL WITH EGC CONTROL
(SEE FLOW CHARTS ON THE FOLLOWING TWO PAGES):
1 - When disconnect is closed, 120V is routed through door
interlock switch (S51) to feed the line voltage side of the
ignition control (A3) and transformer T1 primary. Door inĆ
terlock switch must be closed for A3 and T1 to receive
voltage.
2 - T1 supplies 24VAC to terminal 24VAC" on A3. In turn,
terminal R" of A3 supplies 24VAC to terminal R" of the
indoor thermostat (not shown).
3 - When there is a call for heat, W1 of the thermostat enĆ
ergizes W of the ignition control with 24VAC.
4 - CAB of the ignition control energizes the combustion air
inducer (B6). When the combustion air inducer
nears full speed, combustion air prove switch (S18)
closes. Switch must close within 2 1/2 minutes or
control goes into 5 minute Watchguard Pressure
Switch delay.
5 - When S18 closes, assuming primary limit (S10) and
secondary limit (S21) are closed, a 15 second pre-purge
begins. After the pre-purge period the ignition control
starts ignition spark and opens main gas valve.
6 - After 45 seconds, ignition control (A3) energizes the
indoor blower (B3).
7 - When heat demand is satisfied, W1 of the thermostat deĆ
energizes W of the ignition control and the gas valve is
immediately deĆenergized. The combustion air inducer
immediately stops. The indoor blower runs for a desigĆ
nated fan off" period (60-240 seconds) as set by jumper
on ignition control.
