Which of the following can lead to poor indoor air quality in A/C systems?

Poor indoor air quality in A/C systems can be significantly impacted by dirty air filters. Air filters are designed to capture dust, debris, pollen, and other airborne contaminants. When these filters become clogged with particles, their efficiency in trapping pollutants decreases. As a result, these contaminants can circulate throughout the indoor space instead of being filtered out, leading to deteriorated air quality.

Dirty air filters can also cause additional complications within the A/C system itself. They restrict airflow, making the system work harder to maintain desired temperatures, which could lead to increased energy consumption and potential damage to the system over time.

In contrast, high refrigerant levels and low outside humidity do not directly affect indoor air quality through the same mechanism. High refrigerant levels typically relate more to system performance and efficiency rather than air purity. Similarly, efficient duct design contributes positively to system performance and airflow management, thereby supporting better air distribution and quality rather than detracting from it.