How To Prevent Mold in a Window Air Conditioner? (5 Step Guide)

Want to prevent mold in your window air conditioner, before it becomes a problem? We’ll show you how!

In this proHVACinfo guide, you’ll learn…

  • What causes mold in a window air conditioner
  • Window air conditioner features that help prevent mold
  • What to do if there’s already mold in your window air conditioner

What You Need To Know About Mold in a Window Air Conditioner

If you’re reading this article, chances are you’re thinking ahead about the impact mold can have on your window air conditioner and on your health (or maybe you’ve already had this experience firsthand!).

You’re smart to think ahead. According to the Environmental Protection Agency (“EPA”), potential health effects of mold exposures can include allergic reactions and asthma in those who are sensitive, as well as other respiratory issues.

What’s more, preventing mold is the best way to ensure your a/c unit lasts for years to come (and can avoid an expensive replacement!)

What Causes Mold in a Window Air Conditioner?

The simple answer here is: moisture. This fact alone makes your window air conditioner an easy target for mold, since the air conditioner draws water moisture out of the air as it runs (which is why you may occasionally hear a dripping sound coming from the unit).

This moisture, combined with the dark ducts inside the unit can make for an ideal mold environment. What’s more, mold reproduces via spores, which are microscopic and carried through the air.

For this reason, it’s best to proactively prevent mold from ever growing inside your a/c unit (the EPA recommends not even running an air conditioner that may have mold in it since it may spread spores throughout your home.

Step 1: Keep an eye on humidity

Humidity is a natural cause of moisture which, in turn, is the main cause of mold. The Center for Disease Prevention and Control (“CDC”) recommends indoor humidity in the range of 30% – 60% to discourage mold growth.

Window air conditioners often share some properties with dehumidifiers, but if relative humidity exceeds 60%, you’ll likely find that the air conditioner is ineffective in controlling humidity.

If you find the air humid even when the air conditioner is running, the CDC suggests a dehumidifier to help you keep humidity under control.

Step 2: Don’t let your air conditioner idle

Once your window air conditioner is set up, it’s important to keep the unit running frequently to help prevent mold.

One common mistake people make with their air conditioning unit is to let it idle (that is, they let it sit in the window without actually running the unit) for extended periods – think about when you’re off on a trip to the beach during those hot summer months!

You may think you’re being thrifty by keeping your electric bill down, letting that air conditioner idle completely shuts off the air flow running through the air conditioner, which can let that moisture build up and cause mold.

Instead, we recommend running your air conditioning on a low setting while you’re away (or even better, taking the time to clean out the unit prior to leaving.)

Step 3: Remove dust from the unit

Those mold spores we talked about earlier can also settle in dust inside your air conditioner. There are two places where dust is most likely to settle: on the filter or inside the unit itself.

Removing any lingering dust is as simple as running a hand-held vacuum or vacuum hose inside the air conditioner.

To access the inside of the air conditioning unit, simply remove the front cover. This is a little different for each type of air conditioner, but generally the front cover of the air conditioner will either be “spring-loaded” so you can remove it with your hands or latches you release with your hands. Worst case scenario, you may need to remove a few screws to get the front cover off.

Be sure your air conditioner is unplugged before attempting to access the inside!

We also recommend taking pictures as you go so you’re sure how the unit looked and fit together originally.

Step 4: Remove dust from the filter

The filter for your air conditioner looks like a fine screen inside a plastic frame. It catches debris and air particles to prevent them from circulating into the room.

The filter is a necessary part of the air conditioner, but the dust that accumulates on the filter can make it easy for mold to grow.

The filter is always found just behind the front grill and is typically reusable. To remove dust from the filter, simply run your hand-held vacuum or vacuum hose along the filter (being careful not to damage the mesh screen).

Alternatively, you can place the filter under running water to remove the dust (but wait for it to dry before putting it back into the air conditioner).

Step 5: Regularly clean your air conditioner

The best way to prevent any significant dust and moisture buildup throughout your air conditioning unit is to clean the unit once every few weeks. Learn how to deep clean your air conditioning unit here!

Stephen Marks

Stephen Marks

Stephen is an HVAC and home-repair enthusiast. He's here to answer any of your questions about HVAC!

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Stephen Marks

Stephen Marks

Stephen is an HVAC and home-repair enthusiast. He's here to answer any of your questions about HVAC!

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