Mold In Air Conditioner: How To Clean And Prevent Moldly AC units

Air conditioner units provide the perfect circumstances for mold growth. They are damp, stay at a low temperature and they have plenty of food from organic matter being pulled into the unit.

If left for long enough, the mold will produce spores that can travel through a property and cause more patches around the home, and can cause allergic reactions in people sensitive to them.

In this article, we will cover the topic of mold in air conditioners, how to do it correctly, how to do it safely, and how to prevent it from coming back, so keep reading.

mold air conditioner

How to inspect ac units for mold growth

Before you begin inspecting your ac or HVAC unit, you should look around your home for obvious signs of mold accumulation.

Check the supply vents

Take care to inspect the areas around your ac vents, look for any changes in color, blotches, or black circular marks appearing around the vent.

You can then use a screwdriver to remove the vent cover, allowing you to take a look inside the ducting system behind. Again, you will be looking for any obvious signs of mold accumulation or musty smells.

Check the unit itself

Before opening the unit, check the exterior of the air conditioner to look for any visible signs of mold growth. It is possible for water to condensate on the outside of a unit, which could lead to mold growth. This also gives you the opportunity to check if there is any damage (broken connections for example).

Once you’re certain there is no damage and the exterior of free of mold, you can open the unit to look inside.

If you are not confident doing this yourself, it may be best to hire a professional or call the manufacturer of the unit as if you cause any damage to the unit as a result of your inspection, you may invalidate the warranty.

To check the unit yourself, make sure the unit is switched off and open it, removing the air filter. Visually check these for any signs of mold or mildew.

Check the interior of the unit to ensure there is no visible mold growth, a flashlight may be necessary to be able to see into the deeper parts of the unit.

Check the evaporator coils, as this is where condensation tends to accumulate, making it a prime location for mold growth.

Bear in mind that there are several moving parts within an ac unit, and in some instances, these will be encased, so there may be mold growing in parts that you cannot see from an inspection yourself.

Most ac units will have a water reservoir to collect any water droplets from condensation build-up. Check this tray and empty it if required.

Finally, you should check the intake filters at the back of the unit (on the outside of the unit for a window ac unit) to see any visible signs of mold.

If after an inspection you feel the unit is clear, but you still have a musty smell when the unit is working, you may need to hire an expert to perform a deeper inspection.

What are the symptoms of mold and mildew in an ac unit?

Being able to see spots and blotches on your air vents and ac units is a surefire way of determining whether you have mold in air conditioner, but there are other, less obvious signs that may signal a mold infestation.

Physical symptoms

Mold’s spores can affect people in various ways, for some, they will experience itching eyes, sneezing, and coughing when in contact with mold spores.

For others, the symptoms can be far more serious, leading to breathlessness, asthma attacks, and nausea.

If these symptoms become more frequent whilst the air conditioner unit is turned on, there is a good possibility that mold has accumulated within the unit, and is being passed through the property.


One of the most noticeable signs is a musty scent in your air conditioner that permeates through your property once the unit is switched on.

The smell of mold is often compared to that of old socks or the inside of a caveso it’s not something that can be easily missed.

Is AC mold harmful?

Molds produce allergens by way of spores traveling through the air which are then inhaled, this causes breathing difficulties, asthma attacks, and skin irritation to people sensitive to them.

However, certain molds, including Stachybotrys chartarum (black mold), can produce cytotoxins, which can be much more harmful, for this reason, finding black mold in your air conditioner system is a major issue that needs to be corrected asap.

Symptoms of cytotoxins from molds include:

  • Poor memory function
  • Anxiety
  • Abdominal pain
  • Weight loss and weight gain
  • Numbness
  • Digestive issues

Mold spores passed through your air conditioner unit and around your property can certainly negatively affect people living within the property, especially if the mold exposure is prolonged.

How to remove and kill mold in your air conditioning unit

To effectively kill mold in an air conditioner unit, in a safe and effective manner, use the following cleaning tips:

  • Turn off your air conditioner
  • Remove panels and vents
  • Apply non-diluted white vinegar to the affected surface
  • Leave the vinegar solution to sit for 10 minutes
  • Wipe the area with a cloth until completely dry
  • Leave the unit for up to 24 hours before turning it back on to ensure it is completely dry

The benefit of using vinegar over bleach or hydrogen peroxide is that it is both non-toxic and highly effective at killing mold spores due to its acidity.

There may be a slight residue odor, but this will only last a short period of time.

If there are hard-to-reach areas in your air conditioning unit, you may need to either have it professionally cleaned or replace the unit if the mold is well established.

What kills mold in an air conditioner?

There are several substances you can use to kill mold effectively and safely within your air conditioning unit. These include:

  • Vinegar
  • Baking soda
  • Natural sunlight exposure
  • Hydrogen peroxide
  • Detergent

It is recommended to use products such as vinegar and baking soda to clean mold from an air conditioner, as these are effective at removing mold without releasing harmful chemicals into the air.

If possible, try to get natural sunlight into the unit at least once per month for a few hours. Open the unit to allow natural sunlight in, as the UV rays will kill mold spores. This is an effective, safe, and environmentally friendly method of mold removal.

Can you use bleach to clean an air conditioner?

Using bleach and other harsh chemicals is not recommended for use in ac or HVAC units, as they can cause damage to the contents of the unit and can be hazardous to health if inhaled after being spread through the air. If for whatever reason you find yourself with no choice but to use bleach, ensure you clean the unit using gloves, a mask, and wearing eye protection.

Clean the unit in a well-ventilated area when the unit is switched off, then use the following steps.

Mix 1 part water to 1 part bleach and apply to the affected areas. Leave to sit for 5-10 minutes and clean off with a damp cloth making sure to remove any residue. Leave the unit to dry naturally for several hours before attempting to turn it back on.

Allow as much air into the room whilst the unit is drying, as this will help to remove any fumes from the bleach.

Why does mold grow in ac vents and units?

Mold thrives in moist, dark areas of a property. Air conditioning and HVAC units are perfect for mold to grow as there is a constant source of moisture from condensate (water droplets) after cool air from the unit meets with warmer external air.

Dead skin cells that also travel through the air and other debris also act as a good source for the mold to feed on, so all the requirements for mold to thrive are met within an air con unit.

How to prevent mold growth in air conditioners

Mold does not have to be inevitable within an air conditioner, there are steps and preventative measures you can put in place to make it highly unlikely that you will have to deal with this problem.

Use the following steps to prevent mold accumulation in your ac or HVAC unit.

Clean filters regularly 

Filters by their nature capture dust and debris. These are primarily made up of skin cells and other organic matter that mold can feed on.

Empty water reservoirs

Some ac units and HVAC systems will come with water collection reservoirs to allow liquid to be removed easily from the unit. If your unit has this, make sure you empty it on a regular basis.

Keep the unit running

Mold spores thrive in environments with little to no airflow, so when you turn off your ac unit for several days, you are creating the perfect atmosphere for mold growth.

Clean the unit frequently 

Cleaning the filters is important, but so is cleaning the unit itself. Mold spores can travel very easily within a unit and ducting system, so if care is not taken to ensure it is cleaned at least once every few months, you could easily find your entire home air conditioning system filled with mold.

Which air conditioner units are most likely to grow mold?

You can find mold growing in almost any kind of ac unit if the conditions are correct. As long as there is moisture, a lack of sunlight, and a good source of nutrients, mold can grow.

However, units that are less accessible are more likely to grow mold than window units (for example), as they are harder to inspect manually and may be done so less frequently as a result.

Which molds are most likely to grow in an Air conditioning unit?

There are hundreds of mold variations, but certain strains are more commonly found within the home, especially within air conditioning units.

The most common types of mold you would expect to find in ac units include:

  • Alternaria
  • Aspergillus
  • Acremonium
  • Fusarium
  • Stachybotrys
  • Mucor

Should you remove mold from an ac unit yourself or hire a professional?

Smaller units can be cleaned without the need to hire a professional. These are mostly window-type units where you can easily access the filters and internal components.

For larger units, a professional may be required to give a thorough inspection and deep cleaning.

Further consideration is required when ducting systems are in place, as reaching the affected areas is more difficult and would require professional cleaning equipment to ensure the entire system was clear of mold.

This may still be the case with smaller air conditioners, as there can be inaccessible points where mold can accumulate. In the most severe cases where mold has been allowed to accumulate over a considerable time, replacing the unit entirely may be necessary.


Removing mold from an air conditioner can be complicated depending on the make, the location of the unit, and the unit type. However, for window ac units, you should be able to remove mold yourself fairly easily.

You should take caution when trying to clean your own unit, as there can be hazardous chemicals involved and you also run the risk of damaging your unit if the proper care is not taken. It is for that reason, that if you are not 100% confident, it might be worthwhile having a professional take a look for you.

Chris Walker

Chris Walker has struggled for several years with mold after buying his own property. After finding the solutions to several issues around his home, he decided to create this site in order to answer as many questions about mold and mildew as possible to help others dealing with the same problems.

Recent Posts