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Sequence of Operation HPXA19−024/060
First Stage Cool (low capacity)
Transformer from indoor unit supplies 24VAC power to
the thermostat and outdoor unit controls.
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 passes through high pressure switch S4 and
discharge thermostat switch S5 energizing compres-
sor contactor K1.
HPXA19−024
− Compressor begins start up. Relay
K31 remains closed during start up and capacitor
C7 remains in the circuit. As compressor speeds up
K31 is energized, de−energizing capacitor C7.
3− K1−1 N.O. closes energizing compressor B1 and out-
door fan motor B4. Transformer T46 is also energized.
4− Solenoid L34 is NOT energized. The slider ring re-
mains open limiting compressor to low capacity.
Second Stage Cool (high capacity)
5− Second stage thermostat demand energizes solenoid
relay K195. K195−1 closes sending voltage to rectifier
plug D4. D4 converts the AC voltage to DC voltage and
energizes L34 unloader solenoid. L34 then closes the
slider ring, allowing the compressor to operate at high
capacity.
Heating
A− Ambient temperature ABOVE S23 low ambient
thermostat setting. S23 remains open.
1− Internal wiring de−energizes terminal O by heating
mode selection, de−energizing the reversing valve.
Heating demand initiates at Y1.
2− 24VAC passes through high pressure switch S4 and
discharge thermostat switch S5 energizing compres-
sor contactor K1.
3− K1−1 N.O. closes, energizing compressor, outdoor fan
motor and transformer T46.
4− Solenoid L34 is NOT energized. The slider ring re-
mains open limiting compressor to low capacity.
B− Ambient temperature BELOW S23 low ambient
thermostat setting. S23 closes shunting Y1 and Y2.
1− Internal wiring de−energizes terminal O by heating
mode selection, de−energizing the reversing valve.
Thermostat calls for heating demand.
2− 24VAC passes through high pressure switch S4 and
discharge thermostat switch S5 energizing compres-
sor contactor K1.
3− K1−1 N.O. closes, energizing compressor, outdoor fan
motor and transformer T46.
4− Heat demand energizes solenoid relay K195. K195−1
closes sending voltage to rectifier plug D4. D4 con-
verts the AC voltage to DC voltage and energizes L34
unloader solenoid. L34 then closes the slider ring, al-
lowing the compressor to operate at full capacity.
Defrost Mode
When a defrost cycle is initiated, the control ener-
gizes 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 de-
frost 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 100°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 meth-
ods 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
34−minute Time/Temperature mode.
