The all-in-one direct expansion air purification unit allows the refrigerant to undergo heat exchange directly with the air to be treated, without undergoing secondary heat exchange, i.e., refrigerant-air. In contrast, the currently common large-scale central air conditioning systems, which are composed of chilled water units and air conditioning terminal units, have a different heat exchange method from the direct expansion air conditioning units, which is: refrigerant-water-air. That is, the refrigerant absorbs heat from the water first to generate chilled water, which is then transported through pipelines to the room's fan coil units and other terminal units. The fan inside the unit circulates air, causing the indoor air to exchange heat with the chilled water inside the coil, producing "cool air" that is blown out.