Lennox Harmony III

DUAL FUEL
Page 51
HARMONY IIIT ZONE CONTROL SYSTEM
TroubleshootingDefrost Operation
Defrost
control detects
need for defrost
cycle
?
Yes
No
Yes
Harmony III
control energizes
all compressor
stages
Heat Pump
enters defrost
Defrost
completed
?
No
Yes
Harmony III control
de−energizes all
compressor stages − uses
auxiliary heat to complete
existing heat demand
Defrost
period exceeds
20 minutes
?
No
De−energize
all compressor
stages
Yes
No
NORMAL
HEAT PUMP
OPERATION
Heating
demand
satisfied
?
Dual Fuel
?
Yes
No
Harmony III
sends signal to
W1 at indoor unit
Defrost
Tempering
?
Yes
No
HP cycles W1 OFF at
90ºF and ON at 80ºF
during defrost cycle.