A truck air dryer can fail for several reasons. One of the most common is excessive moisture overload, which oversaturates the desiccant, which in turn reduces drying capacity. The air dryer may not work as intended if contaminants like dirt, oil, or debris clog its internal components. Sometimes, electronics malfunctions can interrupt the regeneration cycle, affecting control systems. Destructive aging, which is most common in high-mileage trucks, usually leads to parts failure in the dryer air.