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Operating Sequence HP27
NOTE− Transformer in indoor unit supplies power
(24VAC) to the thermostat and outdoor unit controls.
COOLING
1 − Internal wiring energizes terminal O by cooling mode
selection, energizing the reversing valve. Cooling de-
mand initiates at Y1 in the thermostat.
2 − 24VAC energizes N.C. high pressure limit S4 which
energizes compressor contactor K1.
3 − K1−1 N.O. contacts close energizing compressor B1
and outdoor fan motor B4.
4 − Compressor B1 and outdoor fan motor B4 begin im-
mediate operation.
HEATING
5 − Internal thermostat wiring de−energizes terminal O by
heating mode selection, de−energizing the reversing
valve. Heating demand initiates at Y1.
6 − 24VAC energizes N.C. high pressure limit S4 and
compressor contactor K1.
7 − K1−1 N.O. contacts close energizing compressor and
outdoor fan motor.
8 − Compressor B1 and outdoor fan motor B4 begin im-
mediate operation.
DEFROST MODE
9− 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.
10− Defrost control CMC1 begins timing. If defrost
ther−mostat (S6) remains closed at the end of the
30,60 or 90 minute period, defrost relay energizes
and defrost begins.
11 − 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.
12 − Defrost continues 14 + 1 minutes or until thermostat
switch (S6) opens. When defrost thermostat opens,
defrost control timer loses power and resets.
13 − When CMC1 resets, the reversing valve and W1 on
the terminal strip are de-energized, while the outdoor
fan motor B4 is energized.
14− After each thermostat demand, time delaylocks out
the circuit to compressor contactor coil and defrost
control for 5 m 2 minutes. At the end of the
timed period, the time delay allows the compressor
contactor and defrost control to be energized upon de-
mand as in step 1.
