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Sequence of Operation LGH180U, 240U, 300U
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. See Staged No Bypass and Staged With Bypass next
2 pages.
ECONOMIZER OPERATION:
4. The A55 Unit Controller receives a demand and ener-
gizes exhaust fan relay K65 and K231 with 24VAC at
50% (travel) outside air damper open (adjustable).
5. N.O. K65-1, K65-2, K231-01 and K231-02 close, ener-
gizing exhaust fan motors B10 and B11.
1ST STAGE COOLING
6. First stage cooling demand energizes Y1 and G in the
thermostat. G energizes blower, if blower is not already
running (see step 3).
7. 24VAC is routed to the A55 Unit Controller. After A55
proves N.C. low pressure switch S87, N.C. freezestat
-
ture limits S5 and S8, compressor contactors K1 and
K2 are energized.
8. N.O. contacts K1-1 and K2-1 close energizing com-
pressor B1 and B2.
-
control logic.
10. Transformer T5 energized outdoor fans B4, B5 and
and B24.
compressor 1 and 2 crankcase heater HR1 and HR2.
2ND STAGE COOLING
12. Second stage cooling demand energizes Y2.
13. 24VAC is routed to A178 Compressor 3 and 4 Control-
N.C. freezestat S53, and N.C. high pressure switch
S28, hight temperature limits S31 and S180, compres-
sor contactors K14 and K146 are energized
14. N.O. contacts K14-1 close energizing compressor
B13.
15. N.O. contacts K146-1 close energizing compressor
B20.
16. N.C. contacts K233-2 and K234-01 open de-energizing
compressor 3 and 4 crankcase heater HR5 and HR11.
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