How does an after cooler or refrigerant dryer remove vapor, water, or oil?

The correct choice highlights the function of an after cooler or refrigerant dryer in the context of removing vapor, water, or oil from a compressed air system. By passing the air through a refrigerant condenser, it effectively lowers the temperature of the air, which in turn reduces the dew point. This cooling process causes moisture in the air to condense into liquid water, allowing it to be separated and removed from the air stream.

This mechanism is crucial because without such temperature regulation, excess moisture could lead to issues in painting and refinishing processes, such as causing defects in the finish or promoting corrosion in the air tools and equipment. The effective lowering of the dew point ensures that the compressed air remains dry and free of contaminants that could compromise quality.

In contrast, the other methods mentioned—heating the air, filtering with compressed media, or spinning the air—do not address the direct condensation of moisture through cooling, which is a central function of a refrigerant dryer or after cooler in air treatment systems. Each of those alternatives lacks the targeted approach of using temperature reduction to handle water vapor, making the correct answer significant for understanding air moisture control in painting and refinishing.