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Why Is My Air Conditioner Air Filter Black?

Why Is My Air Conditioner Air Filter Black?

It is common knowledge that we need to check, clean and replace (if necessary) the air filter of our air conditioning unit every now and then to ensure that it is free from dust and dirt that can affect its performance. 

However, a lot of people neglect to do this causing a lot of problems with their AC units in the long run according to Eastern Air Conditioning, who provides quality air conditioning in Caringbah. Some of these people have even encountered a situation where the air filter of their air conditioning unit has become black forcing them to panic and ask for help from professional repairmen. 

This type of situation is quite alarming and a lot of them are wondering and asking questions why their air conditioner air filter has turned black.

Three of the Most Common Reasons Why an Air Conditioning Air Filter Turns Black

The truth is that there are a lot of reasons why an air filter turns black. However, three of the most common and probable reasons why an air filter has turned black are the following:

Black Soot

According to Clayton’s website, black soot can be a product of various household items like candles and gas water heaters. It is created as a result of incomplete combustion that happens when the oil in a candle or a kerosene lamp doesn’t burn completely, forcing it to mix with the air, which then turns into a black colored substance that we commonly call black soot.

Black soot can quickly turn the air filter of your air conditioning unit black. However, this can also be easily prevented by simply doing any of the following steps:

  • Trim the wick of your candles to a quarter of an inch before lighting it
  • Use candles that are made from all-natural materials
  • Limit the flow of air around any lit candles
  • If you don’t use any candles, check your gas water heater for problems that may cause black soot, like dirty burners, lack of oxygen, and debris


Based on the information provided by the EPA, molds can appear in any place where oxygen and moisture are present. For this reason, our air conditioning units can be a place where molds can appear because of the condensation process in its evaporator coil, which in turn will become moisture that can be transferred to your air filter where molds can begin to develop.

If mold growth is the reason why your air filter turned black then you need to immediately replace your air filter with a new one and dispose of the one that is infected with mold to avoid any health problems that may occur.

Clogged Air Filter

Now, if it is not caused by either black soot or mold, then the most probable reason why your air filter is black is because of severe clogging.

A clogged air filter would not be able to properly prevent the flow of dirt, debris, and other impurities causing a restriction of the airflow which can severely damage your air conditioning unit.

If this happens, you need to clean (if it is still possible) or replace your air conditioner air filter with a new one.

Negative Effects of a Black Air Filter

An air conditioner air filter that is black can cause the following problems:

High Electricity Bills

A black air filter can cause your air conditioning unit to run continuously for longer periods of time causing your energy consumption to go up which will result in higher electricity bills.

Reduced Air Quality

The purpose of your air conditioning unit’s air filter is to prevent unwanted particles like dirt and dust from entering your AC system. The soot, mold, or debris that blocks your air filter will reduce the airflow into your air conditioning unit which will in turn lower the quality of the air that it supplies into your home.

Increased Temperature

A black air filter is an air filter that is clogged with soot, mold, or other debris and pollutants. A clogged air filter will produce a significantly lower circulation of air throughout your home, decreasing its ability to provide cool air which will result in an increase in your room temperature.

Lower AC Unit Efficiency

An air conditioning unit with a clogged air filter will need to operate harder and longer than an air conditioning unit that has clean filters. A black air filter will force your AC units to run longer in order to keep the room temperature inside your home cool and comfortable.

Final Words

The three of the most common reasons why your air conditioner air filter has turned black is because of black soot, molds, and clogged air filters. For these reasons, it is recommended that you clean your air conditioner air filter every 15 days or replace them monthly to prevent the occurrence of a black air filter and to avoid any build-up of dirt, debris, and other harmful elements.