| Aftercoolers An aftercooler is a heat exchanger, which cools the hot compressed air to precipitate the water that otherwise would condensate in the pipe system. It is water or air cooled, generally equipped with a water separator with automatic drainage and should be placed next to the compressor. 80-90% of the precipitated condensation water is collected in the aftercooler's water separator. A common value for the temperature of the compressed air after the aftercooler is approx. 10°C above the coolant temperature, but can vary depending on the type of cooler. An aftercooler is used in virtually all stationary installations. In most cases an aftercooler is built into modern compressors.