Lennox ZCC Series Unit Information page 42

ZCC092/150 Sequence of Operation
Power:
1 - Line voltage from unit disconnect energizes
transformer T1. T1 provides 24VAC power to
terminal strip TB1. TB1 provides 24VAC to the unit
cooling, heating and blower controls.
Blower Operation:
2 - Indoor thermostat terminal G energizes blower relay
K117 with 24VAC. N.O. K117 closes, connecting SD
to STF and RL on the A96 VFD Inverter Controller.
RL sets inverter speed to Low or 40 Hz.
1st Stage Cooling (compressor B1 low capacity)
3 - First stage cooling demand Y1 and G are energized
by the thermostat. G energizes blower. 24VAC is
routed through TB1 passing N.C. high pressure
switch S4. Compressor contactor K1 is energized.
N.O. contacts K1 close energizing B1 two-step
compressor into the lower capacity, or step-one.
4 - Optional N.O. low ambient switch S11 closes to
energize condenser fan relay K10. N.O. contacts
K10-1 and K10-2 close energizing condenser fans
B4 and B5. N.C. contacts K10-3 open de-energizing
crankcase heaters HR1 and HR2.
2nd Stage Cooling (compressor B2 is energized)
5 - Second stage cooling demand 24VAC is routed
through TB1 and proves N.C. high pressure switch
S7. Compressor contactor K2 is energized. N.O.
K2 contacts close energizing compressor B2. In
addition to the Compressor Contactor K2, the K264
Medium Blower speed N.O. closes connecting RD
to RM on the A96 VFD inverter controller. Changing
the A96 VFD to operate at Medium Speed or 55 Hz.
6 - Optional N.O. low ambient switch S84 closes to
energizing condenser fan relay K10. N.O. contacts
K10-1 and K10-2 close energizing condenser fans
B4 and B5. N.C. contacts K10-3 open de-energizing
crankcase heaters HR1 and HR2.
3rd Stage Cooling (compressor B1 High Capacity)
7 - Third Stage cooling demand Y3 24VAC is routed
through TB1 and energizes N.O. contacts on K36
relay connecting SD to RH on the A96 VFD inverter
controller. Changing the A96 VFD to operate at
High Speed or 60Hz.
8 - Third Stage cooling demand Y3 24VAC is routed
through TB1 and energizes L34 2-Stage Solenoid
for Compressor B1. Compressor B1 is now
operating at high-capacity.
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