The air-side particulate fouling in the heat exchangers of HVAC applications degrades the performance of cooling capacity, pressure drop across a heat exchanger, and indoor air quality. Indoor and outdoor air contaminants foul heat exchangers. The purpose of this study is to investigate the cooling performance and pressure drop on the air-side particulate fouling of heat exchangers for air conditioners. Air conditioners being used in the field such as inn, restaurant, and office are collected in chronological used order. Test results show 15% decrease of the cooling capacity and 44% increase of the pressure drop for the 7 years air conditioners used in the seaside inn.