Abstract: In a heat pump system having supplemental heat for application to the supply air during periods of defrost operation, a "cold blow" condition is avoided by turning on a supplemental heater and by sensing the temperature of the supply air and responsively turning on additional heat in stages when necessary to maintain the temperature level of the supply air at a comfortable level.

Abstract: A heat pump is provided with a reversible fan motor in its outdoor coil and, after a delay period following initiation of the defrost cycle, the fan is caused to operate in a reverse direction to thereby cause the surrounding air to flow through the outdoor coil in a direction opposite to that in which it flows during the heating mode operation. During this time, the fan is operated at a relative slow speed to thereby prevent the convective flow of heat upwardly, while at the same time causing little, if any, flow of ambient air downwardly into the coil.

Abstract: A method of controllably charging a heat pump system with refrigerant until adequately charged for the cooling mode of operation, including checking the outdoor ambient temperature, injecting sufficient refrigerant to sustain safe compressor operation, operating the compressor at higher or lower rates depending upon the detected ambient temperature level and determining when to halt charging by monitoring indoor coil inlet and suction temperature differences in the heat pump system.

Abstract: An electronic control box is provided with an internally disposed vent channel which carries ambient air from a bottom opening to the top portion of the control box. The cooling air is then caused to flow downwardly through the control box and over the electronic components by way of a bottom opening which is fluidly connected by a vent tube to a negative pressure area created by the fan. The flow of cooling air through the control box is therefore promoted while maintaining the water-tight integrity of the box.

Abstract: The control box for a refrigeration condensing unit has a heat sink mounted on its rear side between the control box and the coil assembly, the heat sink being in the flow path of the cooling air flowing in thru the coil such that the heat dissipation therefrom is substantially enhanced. The heat sink has a plurality of fins formed on its rear side, with the fins extending across the relatively narrow width of the heat sink such that the cooling air flows over the entire length of each of the fins and provides a substantially uniform velocity profile along the heat sink vertical axis.