How to Get Rid of Black Mold on Styrofoam in Air Conditioner

Every air conditioner is supposed to have EPS (expanded polystyrene) in it, acting as insulation as well as a filter – so you can’t go without it. With that in mind, in cases of high humidity in the air, mold growth can become quite a serious issue.

Most of the time, styrofoam is mold-resistant – but occasionally, mold may grow on it as well.

To get rid of mold, you will either have to clean it or replace the styrofoam altogether.

This article will teach you how to eliminate mold on Styrofoam in air conditioner and prevent future growth.

Is Mold in Air Conditioner Dangerous?

If small amounts of mold spores form on your air conditioner styrofoam, the chances are that you will not be bothered by mildew. 

Mold and mildew in small quantities are often not very dangerous for the average person in the short run – but in the long run, it may trigger some health issues. 

Black mold in window AC is the kind of mold growth that you need to be aware of. 

When this kind of mold begins growing on your air conditioning system, it can become a problem for those with allergies, asthma, or certain breathing problems. 

Plus, mold growth in your air conditioner can lead to throat irritation, stuffy nose, coughing, as well as skin and eye irritation. 

Since your air conditioning system circulates air throughout the house, it will also spread the mold. This is why you need to make sure you maintain the central air styrofoam clean and well-ventilated. 

With that in mind, people are not the only ones that are affected by mold spores. 

Pets may also be affected by black mold, which is why you may want to address this problem as soon as it appears. Mold can form quickly, but it takes a lot of time to get rid of it.

What Causes the Formation of Mold on Styrofoam in Air Conditioner?

Spraying black mold on styrofoam in a window air conditioner

If you have mold growing inside your air conditioning system, it can be either because of high humidity, low ventilation or dirt accumulation. Once the moisture droplets accumulate on the styrofoam, it can rapidly be transformed into mold.

Let’s discuss the main culprits in details;

  • Dirt on The Styrofoam

If there is dirt inside the window AC, black mold can easily form. This is why you need to keep the AC clean – always.

  • Presence of standing water inside your air conditioner

If you have standing water inside the unit, it may also let the mold go loose. Mold-causing bacteria love moisture, so if your AC is not dry, it may just increase the risk of mold formation.

  • Malfunctioning of the AC Unit 

A malfunctioning AC unit cannot ventilate the room properly, leaving way for moisture to go crazy and for mold to grow

  • Poor positioning and location of the AC

When you are using your air conditioner in a humid location, mold spores will begin to form on the unit. Avoid placing your AC in water spots and highly moisturized places.

Preparation Before Cleaning

Technician inspecting a wall mounted window air conditioner

To clean mold from window air conditioner styrofoam, you need to consider two things: the supply list and then the procedure itself. 

Supply list

The supply list starts even before you begin cleaning the air conditioning unit. Here is what you will need to gather:

  • Safety first

When you clean mold, you expose yourself to unhealthy contaminants. Therefore, you need a face mask and waterproof gloves to protect yourself from moisture and the sharp parts of the unit.

  • Window AC Cleaners

Certain types of dish soap have shown to have antibacterial properties, as well as the ability to prevent mold from forming. 

Bleach can be used, but since it’s rather harsh, not everyone recommends it to clean mold on styrofoam in ACs. 

By putting the dish soap in a spray bottle, you should be able to turn it into a spray cleaner to make your air conditioning system nice and clean. 

  • Cleaning Tools & supplies

Cleaning tools are also important to consider when cleaning your air conditioning ducts. 

You will require a scrub brush (preferably made from nylon), a sponge, spray solution, cloth rags, and a vacuum cleaner that has a crevice tool along with an upholstery brush.

  • Hand tools

In terms of hand tools, you will need a screwdriver set to take your window AC apart. 

How to Clean a Window Air Conditioner Styrofoam

Now that you have all your tools necessary to clean a window air conditioner, you may turn your focus onto the actual unit itself. 

Here is a step-by-step guide on how to clean mold from air conditioners.

Step1: Pick the Spot

When you clean a window AC, the chances are that you will be sitting there for a while. 

Find a well-ventilated place where you can reach every place of the AC easily so that you can remove mold without any issues. 

Step 2: Get Inside the AC

Mold spores can easily get inside the air conditioner, which is why you need to use your screwdriver set to remove the grill and access other AC components. 

Step 3: Vacuum Everything

There’s bound to be a lot of dirt and dust along with the mold; thus you may want to start vacuuming your AC. These units’ crevice tool might help you pick up any dirt or dust that likes to hide away from you. 

Step 4: Brush the Fins

Take the upholstery brush and start brushing the fins from the coils of the air conditioning unit. Brush everything from top to bottom before you begin to remove mold from the rest of the unit.

Step 5: Clean the Fins

Now that you are done brushing the air conditioner fins of dust and dirt, you need to clean them as well. 

Take your cleaner and get it evenly on the fins. Let it sit for about 15 minutes, and before it gets to dry, wipe it using a cloth or rinse with some hot water. 

Step 6: Clean the Front Housing

Just like you need to clean the interior, the front part needs to be cleaned as well. After all, if any mold spores have formed there, it will be enough to allow it to replicate and send it straight to the room. 

Use the cleaner on the cover of the AC just like you used it on the inside. After you allow it to sit, rinse with some hot water or wipe with a wet cloth to remove mold that has remained. 

You may also finish off with a dry rag to ensure the space is no longer humid. 

Step 7: Look Deeper Inside

When you clean an air conditioner, in order to make it super clean, you need to scrub into the ducts. 

Look as far back as you can, and use the mold solution on each spot, one by one – allowing it to sit for about 15 minutes before you wipe it away. 

At this point, you might also want to look at the back and the front of the air conditioner, giving it a general interior one-over. Address the filter and everything else you can find inside the unit. 

Step 8: Clean the Grill and Assemble

Using solution on the grill is crucial as mold can quickly grow there. Once you allow it to sit and clean it, you may cover the inside of the window air conditioner. 


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How to Prevent Styrofoam Mold in Window Air Conditioners

Air conditioning on a white wall
  • Use Fan Mode to Dry the Interior of the AC

Almost every air conditioner should have a fan mode that you must regularly to avoid moisture building up inside the AC units.

  • Clean Your Window AC Once or Twice During the Cooling Season

If you keep your home clean at all times, you won’t need to remove mold so often since you won’t let it form in the first place. 

Cleaning it once or twice during the cooling season should be enough.

  • Remove Dust

Mold tends to feed on the dust inside the unit and uses water and humidity spots to grow even more. 

Therefore, you should occasionally take some time to clean the unit of any potential contaminants. Go all the way back from the filter to the cover.

  • HEPA filters

Every air conditioner has some filter – but usually, a standard filter won’t keep the mold from spreading in your home. 

You can opt for HEPA filters on your unit, as they can hold back smaller particles as well.

  • UV filters

For your home to be safe from mold, you might also want to invest in a UV filter. These filters can kill 99% of bacteria and viruses, which means that mold doesn’t have a chance.

  • Controlling your indoor air quality

Most of the mold from your AC is caused by the situation in your home’s indoor and outdoor environment. 


Use a dehumidifier, as it picks up water from the air. Perhaps you can also clean the mold spots in your home with bleach (or other mold-oriented solutions). 

  • Run Your AC regularly

If you leave your unit off for a long time, it gives mold a chance to form. Make sure to turn it back on now and again to create the right habitat for mold.


Cleaning a window air conditioner from mold and preventing it from growing back is easy – as long as you know the steps to follow.

You don’t always need to use bleach, but instead, make sure the place is well-ventilated and dry. Without the environmental factors, mold will not even stand a chance.

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Ronald Watford, the owner of Quality Home Air Care, is a qualified HVACR technician and manages the team of expert writers on this site. He believes that educating homeowners about HVAC systems is one of the most impactful aspects of his job.