Which condition could lead to high indoor humidity levels in a heat pump system?

High indoor humidity levels in a heat pump system can be significantly influenced by dirty coils. When the evaporator coils are dirty, they can inhibit the heat pump's ability to extract moisture from the indoor air. The evaporator coil's surface is critical for heat exchange; if dust and debris accumulate on the coils, it reduces their effectiveness. This compromised function prevents adequate cooling and dehumidification, leading to increased humidity levels within the home.

Dirty coils may also result in reduced airflow, further exacerbating moisture issues because stagnant air cannot efficiently circulate and be dehumidified. Maintaining clean coils is essential for the optimal operation of heat pumps, as cleanliness directly influences humidity control and overall system performance. This emphasizes the importance of regular maintenance in ensuring that heat pumps operate efficiently in managing indoor comfort.