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SEQUENCE OF OPERATION GAS HEAT FOR
LGH156/300 UNITS
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 air blow-
er relay K13 is energized.
3. N.O. K13-1 contacts close allowing line voltage (or
transformer T3 in 575V only) to energize combustion
air blower B6.
4. After the combustion air blower B6 has reached full
speed, the combustion air proving switch (S18) con-
tacts close. The A55 routes 24VAC through N.C. burner
the combustion air proving switch (S18) to energize the
ignition module A3. After a 30 second delay A3 energiz-
5. As steps 2, 3 and 4 occur, A55 proves N.C. primary gas
is energized.
transformer T13 in 575V only) to energize combustion
air blower B15.
7. After the combustion air blower B15 has reached full
speed, the combustion air proving switch (S45) con-
tacts close. The A55 routes 24VACthrough N.C. burner
the combustion air proving switch (S45) to energize the
ignition module A12. After a 30 second delay A12 ener-
SECOND STAGE HEAT:
demand initiates W2 in the thermostat.
10. A55 will energize the corresponding gas valves GV1
OPTIONAL LOW AMBIENT KIT
(C.G.A. -50°C LOW AMBIENT KIT):
-
trols. At the same temperature, S60 closes and en-
ergizes K125. K125-1 contacts close energizing HR6
Cold Weather Kit electric heat.
closes allowing power to A3 and A12 ignition controls.
At the same temperature, S60 opens and de-energiz-
es K125. K125-1 contacts open de-energizing HR6
Cold Weather Kit electric heat.
will open and de-energize K125. K125-1 contacts will
open and de-energize HR6 Cold Weather Kit electric
will close and allow power to K125.
END OF SECOND STAGE HEAT:
-
gized.
A55.
END OF FIRST STAGE HEAT:
-
gized.
17. Ignition module A3 is de-energized by A55 in turn
de-energizing GV1. Combustion blower relay K13 is
also de-energized. At the same instant, ignition mod-
ule A12 is de-energized by A55 in turn de-energizing
-
ergized.
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