Your Dirty AC Filter Could Be
Contributing to Mold, And Putting Stress On Your AC.

SOME COMMON PROBLEMS CAUSED BY DIRTY AC FILTERS

Extremely dirty filters will not allow air to pass through, so unfiltered air will push it to the side and go around it.

FILTER DISPLACEMENT AND AIR BYPASS PROBLEMS

An extremely dirty neglected filter will not allow air to pass through it. Air will push an extremely dirty filter to the side and go around it. As a result, this condition will allow unfiltered air into your AC system. Inferior quality cheap filters will also result in dirty unfiltered air entering your AC as contaminates will pass through the filter. 

Change AC filters about once each month, or once every few months depending on manufacturers recommendations. More importantly, base it on how often your filter gets dirty. 

CLOGGED INEFFICIENT COILS

If your filter is dirty and allows unfiltered air around or through it, then dirty unfiltered air will clog your coils.  Your home’s warm air cannot touch your cold coils if the coils are coated with a insulating layer of dust. As the AC constantly runs trying in vain to push warm air against cold coils you use more electricity. This will cost you money in cooling bills. 

MOLD AND BACTERIA

The dirt or dust on the evaporator coils will rapidly become food for clean bacterial slime or grey fuzzy Cladosporium mold.  

In addition, contamination will also find its way deeper into the system and contaminate your blower fan, supply plenum, the condensation pan, and AC ducts. 

Anyplace where dust and dirt accumulate, mold and bacteria will grow. 

Cladosporium mold inside a flex round AC duct.

Moldy blower fan.

FROZEN COILS

As the air is slowed down by a dirty AC filter and by contamination on the coils, the slow-moving air will spend much more time inside the AC. Because the cold air is moving slowly, it cannot bring enough warm room temperature air into the AC fast enough. 

As a result, the interior of the AC becomes too cold. The cold coils inside the AC will become colder than they were ever intended to become. 

Condensation water that is always on working evaporator coils freezes until you have thick sheets of ice on the coils. 

As the ice melts the dripping melt water causes mold on your filter or in your AC return. 

What looks like a white PVC condensation pipe is actually ice on this AC unit’s copper suction line pipe. It is a sign that the coils inside the AC are very likely icing up as well.

Melting ice water can drip down and cause the AC return and surrounding walls to become wet and moldy as the ice slowly melts. Here we see a water damaged moldy AC return resulting from condensation water.

MOLDY AC FILTERS

Water dripping off icy coils can wet the filter if the filter is below the coils, and the combination of water droplets and dirt build up on the filter can cause the AC filter to become moldy. 

Can you imagine mold growing on and releasing spores from your AC filter? It’s not common but it happens, I see it at least once a year. Look for round black or green spots on the filter. These are mold colonies. If it happens to you dispose of the filter, your filter has become a small mold spore factory.   

Other issues can result in the coils dripping water onto the filter. It could be due to the coils being new and coated with manufacturers’ oil. Gently spray the coils with soap water, do not scrub hard, just spray.
Or it could be due to the top of the coils being cold and wet and the bottom being warm and dry. For more info click here. 

DIRTY AC FILTERS CAUSING BLOWER FAN STRAIN