If a heat pump functions correctly in cooling mode but not in heating mode, what could be the likely issue?

When a heat pump operates properly in cooling mode but fails in heating mode, one likely issue could be related to the flow of refrigerant, which is essential for the heat transfer process. A stuck check valve or a clogged thermal expansion valve (TXV) screen can disrupt this flow, preventing the system from effectively transferring heat in the heating mode.

The check valve is responsible for ensuring that refrigerant flows in the correct direction during the heating cycle and if it becomes stuck, it can obstruct this essential process. Similarly, if the TXV screen is clogged, it can limit the flow of refrigerant into the evaporator, hindering the system's ability to absorb heat and, as a result, impairing the heating capability.

Together, these components are critical for the refrigerant cycle, and their malfunction can directly lead to a situation where the heat pump fails to provide heating even though cooling operations remain unaffected. Understanding the functions of these components helps in diagnosing issues effectively within the heat pump system.