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Mold in A/C Unit

After undergoing an annual air conditioning inspection, my repairman told me I had mold on the inside of the unit which is in my closet in the house.  Is this type of mold toxic or dangerous to our health or nothing to worry about?

The Money Pit Answer

Mold, fed by moisture and trapped dust, can grow inside air conditioning units. However, you should be aware that not all substances inside A/C systems are in fact mold.  Here's what the EPA has to say about wether yyu should have the system cleaned or not:

According to the EPA, you should consider having the air ducts cleaned if:

There is substantial visible mold growth inside hard surface (e.g., sheet metal) ducts or on other components of your heating and cooling system.

There are several important points to understand concerning mold detection in heating and cooling systems:

Many sections of your heating and cooling system may not be accessible for a visible inspection, so ask the service provider to show you any mold they say exists.

You should be aware that although a substance may look like mold, a positive determination of whether it is mold or not can be made only by an expert and may require laboratory analysis for final confirmation. For about $50, some microbiology laboratories can tell you whether a sample sent to them on a clear strip of sticky household tape is mold or simply a substance that resembles it.

If you have insulated air ducts and the insulation gets wet or moldy it cannot be effectively cleaned and should be removed and replaced.

If the conditions causing the mold growth in the first place are not corrected, mold growth will recur.

1 Answers
Woodbridge Environmental answered 6 years ago

Mold regardless of type can be a concern.  Removal of it is in many cases very simple procedure.  The prevention of it not so much.


Mold needs three things in order to develop. 

1. Moisture,  2. air, 3. food source.   if you remove any one of these things you simply do not have mold growth.   It is quite impossible to remove the air, and the food source can be just as hard.  So that leaves just moisture or water.


The only place mold should be found is on cheese or outdoors.  It does not belong in a home and when it does show up its a sign that you have a moisture issue. And with all of the cleaning you can do to make it right will only result in it coming back if you do not stop the moisture or do something to prevent the re-development of it.


In your case the moisture comes from the inside evaporator coil creating condensate.  If your filter system does not trap all of the dust, and most do not do this very well, the dust moves up to the wet coil area where it begins to stick on the damp fins of the coil.  The result over time is mold.


You should consider having the coil cleaned, and if your suffering from health issues have the ducts checked and cleaned if they are really dirty. But read the post that Tom placed prior to this on what the EPA suggests. As most duct cleaning is a waste of time and money. 

But cleaning the coil is not only good in prevention of additional mold growth, it helps the AC system work better. 

Once the coil is clean you should consider the installation of a UV In duct air purifier system.  This light will kill bacteria that can develop within the  cooling coil area and prevent development of mold.


But in any case, unless your heath is dictating how much exposure to the mold you can tolerate is, I would not worry to much, but get it cleaned so it does not get any worse.