One factor to consider is air flow through the system. Air conditioning systems are designed to operate most efficiently with the airflow remaining within the designed range. More air flow is not good but is difficult to achieve but low air flow is not good either and is quite easy to achieve. Leaving a dirty air filter in place may result in low air flow and possibly cause the system to malfunction. In some cases, using an air conditioning filter that is too restrictive for your system may cause low air flow problems as well.

In the old days the filters were commonly the fiberglass variety which might equal a MERV 1 or 2. These provide very good flow but not much filtration beyond the sizable particles in the air. They will help to prevent the evaporator from getting too dirty too fast but they don’t do much to improve air quality. On the other end of the spectrum are the MERV 15 or 16 filters which do an excellent job cleaning the air but are too restrictive for most home systems.

If you are wondering what MERV to try keep these recommendations in mind;
 -ASHRAE recommends MERV 6 or higher
 -US Department of Energy recommends MERV 13
 -Leadership in Energy and Environmental Design, LEED recommends MERV 8 at a minimum

Keep the air flow issue in mind and if possible start with a MERV 6 and work up if no system  performance problems are noted. Most importantly, change you air conditioning filters regularly according to the manufacturer’s recommendation.