Which of the following is NOT a function of an air filter in an air conditioner?

An air filter in an air conditioner primarily serves to improve air quality by trapping dust, pollen, and other airborne particles, preventing them from circulating throughout the living space. It also plays a role in keeping the coils clean by catching contaminants before they can settle on the coils, which helps maintain the efficiency of the cooling system. In addition, by allowing for proper airflow and reducing strain on the system, a clean filter can extend the lifespan of the unit.

While noise reduction can occur naturally as a consequence of proper airflow and system functioning, it is not an intended function of the air filter itself. The design and construction of the air conditioning unit, including its components like the compressor and fans, are more directly responsible for the noise levels produced during operation. Therefore, noise reduction is not a primary role of the air filter, making it the correct answer in this context.