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Vl. ELECTRICAL OPERATION
COOUNG CYCLE
With the disconnect on "ON" position, voltage is supplied to the primary of the control transformer and
crankcase heater. The control transformer reduces the voltage from 230 or 208 to 24 volts for the low
voltage and the thermostat circuit. With a single-stage cool/single-stage heat t_Lh_mostat set in the
cooling _o_ition, current is supplied from one side of the 24 volt secondary of the control transformer
to the "R" terminal of the thermostat. The other side of this transformer connects to the main contractor
coil through the high pressure control. When the thermostat calls for"COOLING', current from the "R"
terminal isswitched on tothe =Y" terminal causing the compressor contactor to be energized. The main
contactor closes the contacts in the high voltage circuit. The completion of this circuit will start both
the outdoor fan motor and the compressor.
The indoor fan relay which is internally wired from "G" to "Y" in the thermostat sub-base is also
energized and starts the indoor fan motor. The system will operate normally and begin to cool.
HEATING CYCLE
With the thermostat set in the heating mode, the "B" terminal energizes the reversing valve relay. With
a call for heat the compressor contactor is energized "W" to =Y"through the jumper wire in the control
panel. The indoor and outdoor fan motors are started in the same manner as in the cooling cycle. The
reversing valve is always energized whenever the system switch on the thermostat is in the heat
position. This eliminates the =swish" at the end of each cycle. Only in the de-ice cycle will the "swish"
occur.
VII. RESISTANCE HEATERS
Resistance heaters are available as an optional field-installed accessory for self-contained heat
pumps. Resistance heaters are recommended for areas where winters are severe, because as the
outdoor temperature falls, the amount of heat available in the air decreases, making it more difficult
to capture. This fact of nature causes the heat pump capacity to fall at a time when the heating
requirement rises. Resistance heaters can compensate for this difference in capacity.
Heat pumps with resistance heaters require a single-stage cool/two-stage heat thermostat. With the
two-stage thermostat, the resistance heaters are energized if the thermostat is turned more than two
degrees higher than the indoor temperature, or the indoor temperature falls more than two degrees
below the thermostat setting. The heaters will also be energized during the defrost cycle.
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