What component is typically used in heat pump systems to assist with defrosting?

In heat pump systems, a reversing valve plays a crucial role in the defrosting process. Heat pumps are designed to provide both heating and cooling, and during colder weather, frost can accumulate on the outdoor coils when the system is in heating mode. To maintain efficiency and prevent damage, the heat pump must enter a defrost cycle periodically.

The reversing valve changes the direction of the refrigerant flow within the system, allowing the outdoor coil to become the evaporator (where heat is absorbed) instead of the condenser. By reversing the flow, the refrigerant's heat is directed to the outdoor coil, causing it to warm up and melt any accumulated frost or ice. This process is essential for maintaining the system's performance during winter months.

The other components listed have different functions: a thermal expansion valve regulates the flow of refrigerant to the evaporator, a gas furnace is primarily used for supplemental heating, and an accumulator manages refrigerant flow and prevents liquid from entering the compressor. None of these components serve the specific purpose of facilitating the defrost cycle in heat pump systems like the reversing valve does.