Air Cooled compressed air after coolers cool the compressed air with atmospheric air. The compressed air is cooled to approximately 9◦C, above ambient temperature. This substantially reduces the water and other contaminants in your air supply, as water will be reduce by ½ for every 20 degree reduction in temperature. This moisture is then removed from the system with a separator and drain assembly. A sufficient capacity after cooler can take up to 80% of the moisture present in the compressed air.