Is there really a difference between air conditioner and heat pump sound levels?
In air conditioning mode, an air conditioner and heat pump work in exactly the same manner and there is no detectable sound level difference. High pressure refrigerant is created by the compressor in the outdoor unit which sequentially creates low pressure refrigerant inside the indoor unit evaporator coil. Low pressure refrigerant turns cold, warm air is circulated across the cold coil ultimately cooling the indoor space. In heating mode an air conditioning system employs a gas furnace and the outdoor unit is idle. A heat pump system reverses the system piping flow pumping high pressure refrigerant to the indoor coil. This heats the coil and the structure as air is circulated across the coil. Hence the outdoor unit is operational during the winter months.