If you don't change your air conditioner filter often enough, it can lead to a buildup of moisture and cause mold to form in your ducts. This can result in serious mold infestations. Air conditioning is filtered through the system five to seven times a day, and when the filter becomes clogged, air cannot easily flow through the system. This causes the entire system to have to work harder to distribute heat or air where it's needed, increasing your utility bills as the air runs longer.
When airflow is hindered by a dirty or clogged air filter, your system has to work much harder to cool your home. As a licensed home inspector, I believe that not changing the filter regularly can reduce the life expectancy of your air conditioner from 6 to 12 years. If you notice that your air filters are black every time you change them, you should be concerned. The dust and dirt in the filter or coils can slow down the air, causing it to spend much longer inside the air conditioner.
This can lead to an increase in indoor air pollution, including pollen, VOCs, and allergens. If you are worried about mold, you should also inspect all the vent covers as well as the inside of your indoor air handler with a flashlight. A tall MERV filter with a very tight mesh can be too much for some units, resulting in a situation similar to a clogged air filter, even right after changing it. A good air filter helps prevent dust and dirt from accumulating on all internal components of the unit; a bad one will cause additional wear and tear that can lead to serious maintenance problems in the future.
Neglecting air conditioning filter changes can also lead to mold growth on the vent covers, ducts, and inside the air conditioning controller. To prevent this, take out the filter from the unit, rinse it with water and allow it to air dry completely before replacing it. Advanced filters can last a little longer between cleanings and replacements, so check with the manufacturer for a recommended program. It is important to install filters properly in HVAC systems so they act as a barrier to prevent contaminants and other particles from circulating in the air or reaching sensitive parts of the system.
I have seen cases where multiple filters were installed on the roof but were not maintained properly by their owners who worked for a foreign embassy. Additionally, I often find that HVAC filters aren't even installed correctly and filter caps and slots are missing.
