HVAC
U.S. Air Force Senior Airman Pierre Hill, 19th Civil Engineer Squadron heating, ventilating and air conditioning journeyman, performs an operational check on a portable chiller Aug. 9, 2016, at Little Rock Air Force Base, Ark. Portable chillers are used when a building’s main air and conditioning unit malfunctions. (U.S. Air Force photo by Senior Airman Stephanie Serrano)