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GAS HEAT SEQUENCE OF OPERATION LGH092/150
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.
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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