Lennox LGH094U Unit Information page 75

Power:
1- Line voltage through the S48 unit disconnect, TB2 terminal block, or CB10 circuit breaker energizes the T1 trans­
former. T1 provides 24VAC power to A55 Unit Controller which provides 24VAC to the unit cooling, heating and
blower controls.
2- Line voltage is also routed to compressor crankcase heaters, compressor contactors, the blower motor contac­
tor, condenser fan relays and exhaust fan relays.
Blower Operation:
3- The A55 Unit Controller module receives a demand from thermostat terminal G. A55 energizes blower contactor
K3 with 24VAC.
4- N.O. K3-1 closes, energizing blower B3.
Economizer Operation:
5- A55 receives a demand and energizes exhaust fan relay K65 with 24VAC at 50% outside air damper open (ad­
justable).
6- N.O. K65-1 and N.O. K65-2 both close, energizing exhaust fan motor B10.
1st Stage Cooling (compressor B1)
7- A55 receives a Y1 thermostat demand.
8- 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.
9- N.O. contacts K1-1 close energizing compressor B1.
10- At the same time, A55 energizes condenser fan relays K10 (when N.O. low ambient switches S11 and S84 close)
and K68.
11- N.O. contacts K10-1 close energizing condenser fan B4 and N.C. contacts K10-2 open, de-energizing compres­
sor crankcase heaters HR1 and HR2. N.O. contacts K68-1 close energizing condenser fan B5.
2nd Stage Cooling (compressor B2 is energized)
12- A55 receives a Y2 thermostat demand.
13- After A55 proves N.C. low pressure switch S88, N.C. freezestat S50 and N.C. high pressure switch S7, compres­
sor contactor K2 is energized.
14- N.O. contacts K2-1 close energizing compressor B2.
LGH092/150 SEQUENCE OF OPERATION
Page 75