Defrost Mode - Lennox HP23 Series Manual

A–HP23 P Voltage Operation Sequence
This is the sequence of operation for HP23 "P" voltage
units. The sequence is outlined by numbered steps
which correspond to circled numbers on the adjacent
diagram.
NOTE– The thermostat used may be electromechan-
ical or electronic.
NOTE– Transformer in indoor unit supplies power (24
VAC) to the thermostat and outdoor unit controls.
COOLING:
1 – Cooling demand initiates at Y1 in the thermostat.
Internal thermostat wiring energizes terminal O
energizing the reversing valve L1.
2 – 24VAC energizes compressor contactor K1.
3 – K1-1 N.O. closes energizing compressor (B1) and
outdoor fan motor (B4).
4 – Outdoor fan motor (B4) begins immediate op-
eration.
5 – Compressor (B1) begins start-up. Hard start
contactor K31 remains closed during start-up
and start capacitor C7 remains in the circuit. As
the compressor gains speed, K31 is energized.
When K31 is energized the contacts open and
start capacitor C7 is taken out of the circuit.
END OF COOLING DEMAND:
6 – Cooling demand is satisfied. Terminal Y1 is de-en-
ergized.
7 – Thermostat terminal O is de-energized.
8 – Reversing valve L1 is de-energized
9 – Compressor contactor K1 is de-energized.
10 – K1-1 opens and compressor (B1) and outdoor
fan motor (B4) are de-energized and stop im-
mediately.
FIRST STAGE HEAT:
11 – Heating demand initiates at W1 in the ther-
mostat.
HP23 SINGLE PHASE OPERATING SEQUENCE
Page 17
12 – 24VAC energizes compressor contactor K1.
13 – K1-1 N.O. closes energizing compressor and
outdoor fan motor.
14 – See steps 4 and 5.
END OF FIRST STAGE HEAT:
15 – Heating demand is satisfied. Terminal W1 is
de-energized.
16 – Compressor contactor K1 is de-energized.
17 – K1-1 opens and compressor (B1) and outdoor
fan motor (B4) are de-energized and stop im-
mediately.

DEFROST MODE:

18 – During heating operation when outdoor coil tem-
perature drops below 35_ + 4 _F Defrost Switch
(thermostat) S6 closes.
19 – Defrost control CMC1 begins timing. If defrost
thermostat (S6) remains closed at the end of
the 30,60 or 90 minute period, defrost relay K4
energizes and defrost begins.
20 – N.O. K4-3 closes energizing the reversing valve.
21 – N.O. K4-1 closes energizing W1 on TB1 terminal
strip of indoor unit. Indoor unit operates in the
first stage heat mode.
22 – N.C. K4-2 opens and outdoor fan motor B4 stops.
23 – Defrost continues 14 + 1 minutes or until ther-
mostat switch (S6) opens. When defrost ther-
mostat opens defrost control CMC1 loses
power and resets.
24 – Defrost relay K4 is de-energized.
25 – K4-1 opens and W1 on terminal strip TB1 of
indoor unit is de-energized.
26 – K4-2 closes and the outdoor fan begins operation.
27 – K4-3 opens de-energizing the reversing valve.