Which component is found on a heat pump but not on an AC unit?

A heat pump is designed to provide both heating and cooling by reversing the flow of refrigerant, allowing it to extract heat from the outside air and deliver it indoors during colder months. The key component that enables this reversing function is the reversing valve.

The reversing valve changes the direction of the refrigerant flow within the system, allowing the heat pump to switch from cooling mode to heating mode. This functionality is unique to heat pumps and is not found in standard air conditioning units, which typically only cool. In air conditioners, the refrigerant flow is unidirectional, meaning they do not require a reversing valve, as their operation does not involve heating the interior space.

Understanding the role of the reversing valve is essential for anyone working with heat pumps, as it directly affects the unit's ability to change between heating and cooling modes efficiently. Although expansion valves and compressors are used in both heat pumps and air conditioning systems, the reversing valve is the unique component that distinguishes a heat pump's design and functionality.