Lennox LCH092H Unit Information page 74

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, supply air inverter control,
condenser fan relays and exhaust fan relays.
Blower Operation:
Supply Air Inverter: Refer to Supply Air Inverter or Direct Drive blower diagram and sequence of operation.
Economizer Operation:
3 A55 receives a demand and energizes exhaust fan relay K65 with 24VAC at 50% outside air damper open (ad­
justable).
4 N.O. K65-1 and N.O. K65-2 both close, energizing exhaust fan motor B10.
1st Stage Cooling (compressor B1 or B2)
5 A55 receives a Y1 thermostat demand.
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 or K2 are energized. Note - A55 logic (using input from RT37 and RT38 temperature sensors and
A185 pressure transducer) determines which contactor is energized.
7 N.O. contacts K1-1 or K2-1 close energizing compressor B1 or B2.
At the same time A55 energizes:
All three condenser fans, B4, B5 & B21, on LOW speed.
K191 compressor 1 crankcase heater relay when K1 is energized or K194 compressor 2 crankcase heater relay
when K2 is energized (after A55 proves N.O. low ambient switch S11 is closed).
8 N.C. K191-1 compressor 1 crankcase heater contacts or N.C. K194-1 compressor 2 crankcase heater contacts
open and de-energize compressor crankcase heater HR1 or HR2.
2nd Stage Cooling (compressor B1 and B2 are energized)
9 A55 receives a Y2 thermostat demand.
10The K1 or K2 compressor contactor which was not energized will close.
11N.O. K1-1 or K2-1 relay contacts which were not energized will close. The corresponding B1 or B2 compressor will
operate in tandem with the other compressor.
At the same time A55 energizes:
All three condenser fans, B4, B5 & B21, on HIGH speed.
The K191 or K194 crankcase heater relay which was not energized will close. N.C. K191-1 or K194-1 relay con­
tacts open and de-energize the corresponding crankcase heater HR1 or HR2.
LCH092/152U SEQUENCE OF OPERATION
Page 74