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SEQUENCE OF OPERATION
LGA, LGC, LCA, LCC248/300/360 G J M Y
NOTE − Steps 12, 17 and 27, beggining with 3 compressor 360H" per-
tain only to LGA/LCA360H units equipped with 3 compressors..
Power:
1− Line voltage from TB2, unit disconnect S48, or other factory or field
installed optional power disconnects, such as CB10, energizes trans-
former T1 and T18. Transformer T1 provides 24VAC power to terminal
strip TB34 and T18 provides 24VAC power to terminal strip TB35. The
two terminal strips provide 24VAC power to the unit cooling, heating
and blower controls and thermostat.
2− Terminal strip TB13 is also energized when the unit disconnect closes.
TB13 supplies line voltage to compressor crankcase heaters, com-
pressors, blower motors, and fan motors.
Blower Operation (OCP input must be on):
3− The main control module A55 receives a demand from thermostat terminal
G. A55 energizes blower contactor K3 with 24VAC.
4− N.O. K3-1 closes, energizing blower B3.
Economizer Operation:
5− The economizer control module A56 receives a demand and energizes ex-
haust fan relay K65 with 24VAC at 50% (travel) outside air damper
open (adjustable).
6− N.O. K65-1 and K65-2 both close, energizing exhaust fan motors B10,
B11 and B12.
1st Stage Cooling
7− First stage cooling demand energizes Y1 and G in the thermostat. G ener-
gizes blower, if blower is not already running (see step 3).
8− 24VAC is routed through TB34 to the main control module A55. After A55
proves N.C. low pressure switch S87, N.C. freezestat S49, and N.C. high
pressure switch S4, compressor contactor K1 is energized.
9− N.O. contacts K1−1 close energizing compressor B1.
10−Control module A55 energizes condenser fan contactor K10.
11− N.O. contacts K10−1 close energizing condenser fan B4 and N.C. contacts
K10−2 open de-energizing compressor crankcase heaters HR1 and HR2.
12− 3 compressor 360H − N.O. contacts K10−1 close energizing condenser fan
B4 and N.C. contacts K10−2 open de-energizing compressor crankcase heat-
ers HR1.
13− Simultaneous with step 8, 24VAC is routed through the compressor 2 control
module A57. After A57 proves N.C. low pressure switch S88, N.C. freezestat
S50, and N.C. high pressure switch S7, compressor contactor K2 is en-
ergized.
14− N.O. contacts K2−1 close energizing compressor B2.
15− Compressor 2 control module A57 energizes condenser fan 2 relay K68.
Compressor 3 control module A59 energizes condenser fan relay K149
through N.O. low ambient pressure switches S11 or S84.
16− N.O. contacts K68−1 and K149−1 close energizing condenser fans B5 and
B21.
17− 3 compressor 360H−Compressor 2 control module A57 energizes condens-
er fan 2 relay K68. Compressor 3 control module A59 energizes condenser
fan relay K149 and K150 through N.O. low ambient pressure switches S11 or
S84. A59 also energizes condenser fan relays K152 and K153.
18− N.O. contacts K68−1, K149−1, K150−1, 152−1 and K153−1 close energizing
condenser fans B5, B21, B22, B23 and B24. N.C. contacts K150−2 open de−
energizing compressor crankase heater HR2 and HR5.
2nd Stage Cooling
19− Second stage cooling demand energizes Y2.
20−24VAC is routed through TB35 to compressor 3 and 4 module A59. Af-
ter A59 proves N.C. low pressure switches S98 and S97, N.C. free-
zestats S53 and S95, and N.C. high pressure switches S28 and S96,
compressor contactors K14 and K146 are energized.
21− N.O. contacts K14−1 close energizing compressor B13.
22− N.O. contacts K146−1 close energizing compressor B20.
23−N.O. low ambient pressure switches S85 and S94 close to energize con-
denser fan relay K150.
24−N.O. contacts K150−1 close energizing condenser fan B22.
25− Compressor 3 and 4 module A59 energizes condenser fan relay K152 and
K153.
26−N.O. contacts K152−1 and K153−1 close energizing condenser fan B23
and B24. N.C. contacts K152−2 open de-energizing compressor 3
crankcase heater HR5 and compressor 4 crankcase heater HR11.
27−3 compressor 360H−24VAC is routed through TB35 to compressor 3
module A59. After A59 proves N.C. low pressure switch S98, N.C.
freezestat S53 and high pressure switch S28, compressor contactor
K14 is energized.
28− N.O. K14−1 contacts close energizing compressor B13.
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