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12HPB 1-1/2 THROUGH 5 TON OPERATING SEQUENCE
This is the sequence of operation for 12HPB series units.
The sequence is outlined by numbered steps which corre-
spond to circled numbers on the adjacent diagram.
NOTE− The thermostat used may be electrome-
chanical or electronic.
NOTE− Transformer in indoor unit supplies power (24
VAC) to the thermostat and outdoor unit controls.
COOLING:
1 − Internal thermostat wiring energizes terminal O by
cooling mode selection, energizing the reversing valve
L1. Cooling demand initiates at Y1 in the thermostat.
2 − 24VAC energizes compressor contactor K1.
3 − K1-1 N.O. closes, energizing compressor (B1) and out-
door fan motor (B4).
4 − Compressor (B1) and outdoor fan motor (B4) be-
gin immediate operation.
END OF COOLING DEMAND:
5 − Cooling demand is satisfied. Terminal Y1 is de-ener-
gized.
6 − Compressor contactor K1 is de-energized.
7 − K1-1 opens and compressor (B1) and outdoor fan
motor (B4) are de-energized and stop immediate-
ly.
8 − Terminal O is de−energized when internal thermostat is
out of cooling mode, de−energizing the reversing valve
L1.
FIRST STAGE HEAT:
9 − Heating demand initiates at Y1.
10 − 24VAC energizes compressor contactor K1.
11 − K1-1 N.O. closes, energizing compressor and
outdoor fan motor.
12 − Compressor (B1) and outdoor fan motor (B4) be-
gin immediate operation.
END OF FIRST STAGE HEAT:
13 − Heating demand is satisfied. Terminal Y1 is de-
energized.
14 − Compressor contactor K1 is de-energized.
15 − K1-1 opens and compressor (B1) and outdoor
fan motor (B4) are de-energized and stop imme-
diately.
DEFROST MODE:
16 − During heating operation when outdoor coil tempera-
ture drops below 35_F (2_C) or 42_(5.5_C) see de-
frost system description for specific unit dash number
defrost switch (thermostat) S6 closes.
17 − Defrost control CMC1 begins timing. If defrost
thermostat (S6) remains closed at the end of the
30,60 or 90 minute period, defrost relay energizes
and defrost begins.
18 − During defrost CMC1 energizes the reversing valve
and W1 on the terminal strip (operating indoor unit on
the first stage heat mode), while de-energizing outdoor
fan motor B4.
19 − Defrost continues 14 + 1 minutes or until thermostat
switch (S6) opens. When defrost thermostat opens,
defrost control timer loses power and resets.
20 − When CMC1 resets, the reversing valve and W1 on the
terminal strip are de-energized, while the outdoor fan
motor B4 is energized.
21 − When CMC1 resets, the reversing valve and W1 on the
terminal strip are de-energized, while the outdoor fan
motor B4 is energized.
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