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Sequence of Operation Gas Heat LGM156/300
First Stage Heat:
1 - Heating demand initiates at W1 in thermostat.
2 - 24VAC is routed to the A55 Unit Controller. After
A55 proves N.C. primary limit S10, the combustion
3 -
full speed, the combustion air proving switch (S18)
contacts close. The A55 routes 24VAC through N.C.
contacts of the combustion air proving switch (S18)
to energize the ignition module A3. After a 30
second delay A3 energizes the gas valve GV1 on
4 - As steps 2, 3 and 4 occur, A55 proves N.C. primary
B15 is energized.
5 - After the combustion air blower B15 has reached
full speed, the combustion air proving switch (S45)
contacts close. The A55 routes 24VAC through N.C.
contacts of the combustion air proving switch (S45)
to energize the ignition module A12. After a 30
second delay A12 energizes gas valve GV3 on low
Second Stage Heat:
demand initiates W2 in the thermostat.
7 - A second stage heating demand is received by A55.
8 - A55 will energize the corresponding gas valves
Optional Low Ambient Kit
energizes K125. K125-1 contacts close energizing
10 -
and deenergizes K125. K125-1 contacts open de-
11 -
will open and de-energize K125. K125-1 contacts
electric heat. If heat section temperature drops to
End of Second Stage Heat:
12 -
deenergized.
13 -
A55.
End of First Stage Heat:
14 -
deenergized.
15 - Ignition module A3 is de-energized by A55 in turn
de-energizing GV1. Combustion blower air blower
ignition module A12 is de-energized by A55 in turn
also de-energized.
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