Lennox LGH094U Unit Information page 79

First Stage Heat:
1- Heating demand initiates at W1 in the thermostat.
2- 24VAC is routed through TB34 to the A55 Unit Con­
troller. After A55 proves N.C. primary limit S21, the
combustion air blower relay K13 is energized.
3- N.O. K13-1 contacts close allowing line voltage to en­
ergize combustion air blower B6.
4- After the combustion air blower B6 has reached full
speed, the combustion air proving switch S18 contacts
close. The A55 routes 24VAC through N.C. burner
flame roll-out switch S47 and the closed contacts of
combustion air proving switch S18 to energize the igni­
tion module A3.
5- After a 30 second delay A3 energizes the ignitor and
LO terminal (low fire) of gas valve GV1.
Second Stage Heat:
6- With first stage heat operating, an additional heating
demand initiates W2 in the thermostat.
7- A second stage heating demand is received by A55
Unit Controller.
8- A55 energizes HI terminal (high fire) of gas valve GV1.
GAS HEAT SEQUENCE OF OPERATION LGH092/150
End of Second Stage Heat:
9- Heating demand is satisfied. Terminal W2 (high fire) is
de-energized.
10- Terminal HI of GV1 is de-energized by A55 control
module.
End of First Stage Heat:
11- Heating demand is satisfied. Terminal W1 (low fire) is
de-energized.
12- Ignition A3 is de-energized by control module A55 in
turn de-energizing terminal LO of GV1. Combustion air
blower relay K13 is also de-energized.
Optional Low Ambient Kit:
(C.G.A. -50° C Low Ambient Kit)
13- Line voltage (or transformer T20 in 460V and 575V on­
ly) is routed through the low ambient kit fuses F20 and
N.C. low ambient kit thermostats S60 and S61,to ener­
gize low ambient kit heater HR6.
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