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SEQUENCE OF OPERATION LGA/LCA036/072
Power:
1. Line voltage from unit disconnect energizestransform-
er T1. T1 provides 24VAC power to terminal strip
TB34. TB34 provides 24VAC to the unit thermostast
cooling, heating and blower controls.
2. Line voltage from unit disconnect provides voltge to
compressor crankcase heaters HR1 (through dis-
charge line thermostat on single phase scroll compres-
sors), compressor contactorK1, the blower motorcon-
tactor K3 and condenser fan relay K10.
Blower Operation:
3. The main control module A55 receives a demand from
thermostatterminalG.A55 energizes blower motor cir-
cuit as follows:
4. Belt Drive:
A55 energizes blower contactor K3 with 24VAC. N.O.
contacts K3-1 close, energizing blower B3.
5. Direct Drive:
a) On cooling or fan only demand, A55 energizes blow-
er contactor K3. N.O. contacts K3-1 close energizing
motor B3 on cool tap.
b) On heating demand, A55 energizes combustion air
blower relay K13. N.O. contacts K13-2 close, energiz-
ing heat blower relay K36. N.O. contacts K36-1 close,
energizing blower B3.
Note- Speed selection for Direct Drive motors are
made through lead selection at P43/J43 cap-plug on
B3 motor.
1st Stage Cooling
6. Cooling demand energizes Y1 and G in the thermostat. G
energizes blower.
7. 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, com-
pressor contactor K1 is energized.
8. N.O. contacts K1-1 close energizing compressor B1.
9. N.O. low ambient switch S11 closes to energizecondens-
er fan relay K10.
10. N.O. contacts K10-1 close energizing condenser fan B4
and N.C. contacts K10-2 open, de-energizing compressor
crankcase heater HR1.
Economizer Operation:
11. The economizer control module A56 receives a demand
and energizes exhaust fan relay K65 with 24VAC at 50%
outside air damper open (adjustable).
12. N.O. K65-1 and N.O. K65-2 both close, energizing ex-
haust fan motor B10.
Note- Speed selection for Direct Drive motors are
made through lead selection at P43/J43 cap-plug on
B3 motor.
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