Air-Conditioning Heat Pump Inspection – Items to be Checked
The condenser is located in the house, and when the system is operating, it is cooled by the air that is circulated around the house. As this air passes over the condenser, it absorbs heat that is used for heating the house. The evaporator is located outside the house, and for the cycle to operate properly it must absorb heat from the outside air. Even when the outside temperature drops, the evaporator can still absorb heat because the refrigerant within the evaporator is at a lower temperature. Nevertheless, the ability of the evaporator to absorb heat decreases as the temperature of the outside air drops, thus decreasing the effectiveness of the heat pump as well. A heat pump may be operational at temperatures as low as 20° F, however the Btu output is sufficiently reduced so that additional heaters are usually required.
A heat pump should be sized for the air conditioning load rather than the heating load, otherwise the air conditioner will be oversized. With the exception of a small section of the Deep South, the heating load on a house will always be greater than the cooling load.
A heat pump will produce about 20 percent more Btus per hour for heating than it does for cooling, so in most parts of the country, when a house is heated by a heat pump it often requires auxiliary heaters. In the New York area, for instance, a typical eight-room house would require a furnace able to produce about 100,000 Btus per hour for winter heating, as well as a 31/2 ton (42,000 Btu/hour) air conditioning unit for summer cooling. A properly sized heat pump used for heating would produce just 50,400 Btu/hour, leaving the remaining 49,600 Btu/hour to be provided by auxiliary heaters, which are usually electrical resistance heaters.
When the pump cannot supply sufficient heat to keep up with the heat loss of the structure during the winter, the auxiliary heaters in heat pumps are automatically activated. In communities where there is a significant amount of moisture and low temperatures during the winter, there is a tendency toward an ice buildup on the metal find of the outdoor evaporator coil. If the ice buildup become excessive, it could cut off air circulation across the coil and result in a loss of heating capacity.
With more sophisticated heat pumps, the icing condition is automatically controlled by a defrost cycle that reverses the flow of the refrigerant for a short time, so the hot refrigerant heats the outdoor coil and melts the ice. During the defrost cycle, the auxiliary heaters are usually energized to offset the cycle’s cooling effect on the indoor circulating air.
A heat pump can operate in the heating or the cooling mode, but most manufacturers recommend that the unit be operated in the air conditioning mode when the outdoor air temperature is above 65° F and in the heating mode when the temperature is below that. Operating a heat pump in the wrong mode can result in damage to the compressor, so an air conditioning heat pump inspection will definitely include checking that the proper mode is in use.
The components and problems of air conditioning heat pumps are basically similar to those of air conditioning systems, so the overall inspection procedure for air conditioners should be used for heat pumps as well. However, the inspector should not check both modes of operation. As long as the unit is operating properly in the mode tested, it means that the major (and most costly) components – compressor, fans and coils – are operational, so the system should also function in the opposite mode. If it does not function properly in the opposite mode, usually the cause is a faulty reversing valve.