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Sequence of Operation LGH156/300
POWER:
1. Line voltage from TB2, unit disconnect S48, or other
such as CB10, energizes transformer T1 and T18.
Transformer T1 provides 24VAC power to the A55 Unit
-
pressor 3 and 4 Controller. The two controllers provide
24VAC power to the unit cooling, heating and blower
controls and thermostat.
2. Terminal block TB13 is also energized when the unit
disconnect closes. TB13 supplies line voltage to com-
pressor crankcase heaters, compressors, blower mo-
tors and fan motors.
BLOWER OPERATION (OCP INPUT MUST BE ON):
3. The A55 Unit Controller receives a demand from ther-
mostat terminal G. A55 energizes blower contactor K3
with 24VAC.
4. N.O. K3-1 closes, energizing blower B3.
ECONOMIZER OPERATION:
5. The A55 Unit Controller receives a demand and ener-
gizes exhaust 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 and B11.
1ST STAGE COOLING (BOTH COMPRESSORS B1
AND B2 ARE ENERGIZED):
7. First stage cooling demand energizes Y1 and G in the
thermostat. G energizes blower, if blower is not already
running (see step 3).
8. 24VAC is routed to the A55 Unit Controller. After A55
proves N.C. low pressure switch S87 and S88, N.C.
S4 and S7, compressor contactors K1 and K2 are en-
ergized.
-
pressor B1 and B2.
10. A55 Unit Controller and A178 Compressor 3 and 4
Controller energize fan contactor K10 (all units), K68
only), K152 (210H only), K153 (210H only) based on
control logic.
(180H-300S only), K150-1 (180H/210H only), K152-
1 (210H only), K153-1 (210H only) close energizing
fan B4 (all units), B5 (all units), B21 (all units), B22
(180H/210H only), B23 (210H only), B24 (210H only).
12. Relay contacts K10-1 (210H), K10-2 (156H, 240H,
300S) or K68-1 (180H) open de-energizing compres-
sor 1, 2 and 3 crankcase heater HR1 (all units), HR2
(all units) and HR5 (156H-210H only).
2ND STAGE COOLING (B13 IN 156H-210H AND BOTH
B13 AND B20 IN 240H AND 300S ARE ENERGIZED):
13. Second stage cooling demand energizes Y2.
-
-
tors K14 and K146 are energized.
NOTE:
S28 and K14 only. 15. N.O. contacts K14-1 close energiz-
ing compressor B13.
16. N.O. contacts K146-1 close energizing compressor
B20 (LGH240/300 only).
contactor K150, K152, K153 (240H/300S only) based
-
18. N.O. contacts K150-1, K152-1 and K153-1 (240H/300S
only) close energizing condenser fan B22, B23 and
B24 (240H/300S only).
-
gizing compressor 3 and 4 crankcase heater HR5 and
HR11 (240/300S only).
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