Abstract: An air cooling tower system for condensing exhaust steam in power plants, that has water cooling augmentation to maintain the plant cooling capacity during high atmospheric temperature periods. The cooling tower includes a plurality of banks of brazed aluminum plate and fin type heat exchangers arranged in inverted "V" shaped sets. These heat exchangers cool ammonia used as the cooling fluid in the primary condenser for the power plant turbine exhaust steam. Each of these heat exchangers has a core consisting of a plurality of parallel aluminum plates spaced apart by fin assemblies that define a plurality of fluid passes. Approximately every other one of these passes has closed sides that open at the ends of the core to headers and define ammonia passes. The passes adjacent the ammonia passes are open at the sides and define air passes that permit the free flow of air transversely through the heat exchanger cores.