If a heat pump's reversing valve fails to switch between heating and cooling modes, which component is most likely defective?

• A. Reversing valve
• B. Compressor
• C. Thermostat
• D. Fan motor

Answer: (A)

Switching between heating and cooling in a heat pump is controlled by a reversing valve that changes the direction of refrigerant flow. When this valve fails to switch, the system can’t change modes, so it stays in one mode or won’t respond to a demand for the other. The reversing valve is the component directly responsible for mode selection, which is why it’s the most likely defective part in this scenario.

The other parts don’t align as directly with mode changes: the compressor keeps the cycle going but doesn’t determine which mode is active; the thermostat triggers heating or cooling requests but doesn’t physically redirect refrigerant flow; the fan motor affects airflow and heat transfer rather than the mode itself.