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Sequence of Operation LGM/LCM156 & 180U
1 - Line voltage from TB13 energizes transformer T1 and T18. Transformer T1 and T18 provides 24VAC
power to the main controller A55. The transformers also provide 24VAC power to the unit cooling,
heating and blower controls and thermostat
ECONOMIZER OPERATION
2- The A55 Unit Controller receives a demand and energizes exhaust fan relay K65 and K231 with 24VAC at
50% (travel) outside air damper open (adjustable).
3- N.O. K65‐1, K65‐2, K231-01 and K231-02 close, energizing exhaust fan motors B10 and B11.
1ST STAGE COOLING
4- First stage cooling demand energizes Y1 and G in the thermostat. G energizes blower, if blower is not already
running (see step 3).
5- 24VAC is routed to the A55 Unit Controller. After A55 proves N.C. low pressure switch S87 , high pressure switch
S4 and high temperature limits S5 compressor contactor K1 is energized.
6- N.O. contacts K1-1 close energizing compressor B1.
7- A178 energizes outdoor fans B21 and B22.
8- Relay K191 opens de-energizing compressor 1 crankcase heater HR1.
2ND STAGE COOLING
9- Second stage cooling demand energizes Y2.
10- After A55 proves N.C. low pressure switch S88 and S98, and N.C. high pressure switch S7 and 228, contacotors
K1 and K14 are energized.
11- N.O. K2 closes energizing compressor B2 and de-energizing crankcase heater HR2.
12- N.O. K14 closes energizing compressor B13, de-energizing HR5.
13- A178 energizes outdoor fans B4 and B5.
BLOWER OPERATION With By Pass
1- Control inverter A96 energizes contactor K202 and main control A55 energizes relay 203.
2-
K203-1 N.C. contacts open to de-energize K3 relay coil. K3 contacts open to interrupt power to
B3 blower motor through K3 N.O. relay contacts.
3- K202 contacts close to allow power to B3 blower motor from A96.
BLOWER OPERATION No By-Pass
1- Control inverter A96 energizes B3 on a G demand.
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