Members of the 436th Civil Engineer Squadron, Heating Ventilation and Air Conditioning, and Horizontal Shops, install one of two 60-ton air conditioning chillers for Building 520 Feb. 15, 2013, Dover Air Force Base, Del. Old chillers using R-22 refrigerant were removed and replaced with the new chillers, which use environmental-friendly R-410A refrigerant that does not contribute to ozone depletion. (U.S. Air Force photo/Roland Balik)