Lennox LCH060H4E

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LCH036-074 G, J, P, M, & Y Voltage Sequence of Operation
Power:
1. Line voltage from unit disconnect energizes transformer T1. T1 provides 24VAC power to the A55 Unit Control
ler. A55 provides 24VAC to the unit cooling, heating and blower controls.
2 Line voltage from unit disconnect provides voltage to compressor crankcase heaters HR1 (through discharge
line thermostat) and compressor contactor K1.
A-Belt Drive Units - Voltage is distributed to blower motor contactors K3 (single & two speed systems) and K37
(two speed systems) and condenser fan relay K10.
B-Direct Drive Units: Voltage is distributed directly to blower motor B3 and outdoor fan motor B4.
Blower Operation:
The A55 Unit Controller receives a demand from thermostat terminal G. A55 energizes blower motor circuit follows:
3 Belt Drive:
A-Single-Speed Systems (072 units): A55 energizes blower contactor K3 with 24VAC. N.O. contacts K3-1 close
energizing blower B3.
B-Two-Speed Systems (036, 048, 060 and 074 units): A55 energizes blower low speed contactor K3 with
24VAC. N.O. contacts, K3-1, close energizing blower B3 on low speed (default). A55 can be programmed to
direct 24VAC to blower high speed contactor K37 to energize blower B3 on high speed.
4 Direct Drive:
A-A55, through motor control board energizes blower B3 via programmed motor settings. Motor settings are
field-adjustable.
First-Stage Cooling
5 A55 Unit Controller receives a Y1 and G cooling demand and energizes blower B3 (low speed on two-speed belt
and direct drive blowers).
6 After A55 proves n.c. low pressure switch S87, n.c. freezestat S49, and n.c. high pressure switch S4, compres
sor contactor K1 is energized.
7 N.O. contacts K1-1 close energizing the compressor B1. On two-speed systems (3, 4, and 5 tons) compressor
is energized on low speed.
A-Belt Drive Blowers - S11 n.o contacts close below 62ºF. A55 energizes n.o. contacts K10-1 closed to start
condenser fan B4.
B-Direct Drive Blowers - S11 n.o. contact close below 62ºF. A55 energizes outdoor fan motor B4 on low speed.
Second-Stage Cooling
8 A55 receives a Y2 and G cooling demand and energizes blower B3 (high speed on two-speed belt and direct
drive blowers).
9 On two-speed systems (036, 048, 060 aand 074), A55 energizes compressor solenoid L34, switching compres
sor to high speed.
A-Direct Drive Blowers - A55 energizes outdoor fan motor B3 on high speed.
Power Exhaust Fan Operation
10 A55 receives a position feedback signal from the economizer damper motor and energizes exhaust fan relay
K65 with 24VAC at 50% outside air damper open (adjustable).
11 N.O. contact K65-1 & 2 close, energizing exhaust fan motor B10.