Reversing Valve : A device in a heat pump that is electrically controlled to reverse the flow of refrigerant as the system is switched from cooling to heating; also called a four-way valve
EESiFlo North America, Terminology and Glossary: HVAC Terms, Pennsylvania, USA 2002. flowmeterdirectory.com/flowmeter_terminology, (Heat, Vent and Air Cond - Amer) {553}