In a heat pump system, when is the reversing valve typically engaged?

In a heat pump system, the reversing valve is engaged during cooling mode to allow the system to effectively remove heat from the indoor air and release it outside. When the reversing valve is activated, it changes the direction of the refrigerant flow, enabling the heat pump to absorb heat indoors and expel it outdoors.

In cooling mode, the evaporator coil is located inside the home and acts like a traditional evaporator, absorbing heat from the indoor air. The condenser coil, located outside, expels that heat, effectively cooling down the indoor environment.

The other scenarios mentioned do not require the reversing valve to be engaged in the same way as cooling mode. For instance, during heating mode, the reversing valve's function is already in place to circulate heat indoors, and the thermostat being set to off would not use the valve since the system is not actively cooling or heating. Defrost mode also activates the reversing valve, but that is a specific scenario to prevent frost buildup on the outdoor coil rather than the standard operational mode.