Lennox XP16 Series Unit Information page 50

B – High Capacity (Ambient temperature below
defrost board Y2 lock−in temperature)
1 − Room thermostat in heating mode. Room thermostat
outputs Y1 signal to the defrost board in the heat pump
and to the indoor unit.
2 − The defrost board checks for open low or high−pressure
switches and proper coil, ambient and discharge sensor
readings.
If checks show no issues, the defrost board sends
D
24 volts through Y1 OUT signal to the K1
compressor contactor coil.
XP16−060−05 only − defrost board sends 24 volts
D
through Y1 OUT signal to the yellow wire to the
outdoor fan motor.
3 − The defrost board Y2 locks in sends:
24 volts through Y2 OUT to the L34 compressor
D
solenoid plug.
XP16−060−05 only − 24 volts through Y2 OUT to
D
the blue wire to the outdoor fan motor.
The plug converts the 24volt AC outputs to a 24volt DC
signal input to the L34 internal high capacity solenoid valve
in the compressor.
4 − K1−1 closes, energizing the compressor and outdoor fan
motor through the normally closed fan relay contacts on
the defrost board.
D The compressor runs on high capacity.
XP16−060−05 only − The 24 volt input to the
D
yellow and blue wires of the outdoor fan will
provide high speed operation.
When a defrost cycle is initiated, the control
energizes the reversing valve solenoid and turns off
the condenser fan. The control will also put 24VAC on
the W1" (auxiliary heat) line. The unit will stay in this
mode until either the coil sensor temperature is above
the selected termination temperature, the defrost
time of 14 minutes has been completed, or the room
thermostat demand cycle has been satisfied. (If the
temperature select shunt is not installed, the default
termination temperature will be 90°F.) If the room
thermostat demand cycle terminates the cycle, the
defrost cycle will be held until the next room
thermostat demand cycle. If the coil sensor
temperature is still below the selected termination
temperature, the control will continue the defrost
cycle until the cycle is terminated in one of the
methods mentioned above. If a defrost is terminated
by time and the coil temperature did not remain above
35°F (2°C) for 4 minutes the control will go to the
30−minute Time/Temperature mode.
Page 50
Defrost Mode
XP16