The amount of water vapor in compressed air is determined by the moisture content of the compressed air. When the pressure of the compressed air remains basically unchanged, the air's capacity to hold water decreases as the temperature drops, causing water that was originally in a gaseous state to become liquid. A refrigerated dryer operates based on this dehumidification principle, using a refrigeration system to cool the compressed air to a certain dew point temperature, causing the water vapor to condense into liquid. The air and liquid are then separated by a separator, and the water is discharged through an automatic drain, thereby drying the compressed air. In an air-cooled refrigerated dryer, the cooling system uses an air-cooled radiator, where a fan blows across the high-pressure part of the refrigeration system, and the airflow carries away the heat.