What Kind Of Mold Grows In Window Air Conditioners?

Window air conditioners rarely get moldy. When you find a window air conditioner has mold growing inside of it, it is almost always exclusively because of standing contaminated water.

What kind of mold grows in the window air conditioners.

The 4 most common mold types found in window air conditioners are:

  1. Fusarium
  2. Acremonium
  3. Alternaria
  4. Mucor

What kind of mold grows in the window air conditioners1.  Fusarium

The highest level of fusarium spores occur in the summer months and require wet circumstances. It can grow in stagnant water and in humidifier catch pans.

2.  Acremonium

Acremonium is commonly found in Hay and other dead plant material. It is also found in water damaged building materials and because it needs a very wet environment it also grows in the insulation around air conditioning.
It can easily get its start from cooling coils, standing water in drip pans, or humidifier water.

Acremonium often grows in combination with stachybotry chartarum. The dreaded black mold. Black mold requires extremely wet long-standing conditions.
It is considered one of the major components in sick building syndrome.

3. Alternaria

Alternaria is the most common form of mold found in building materials and is often found in water damaged or flooded areas as well as standing water in humidifiers.

4.  Mucor

Mucor is the chrysalis looking mold that gathers around the condensation on the windowsill of the air conditioner.

Each type of mold listed needs a steady supply of moisture in order to cultivate.
And also each of these types of molds can be found in drip pans or humidifier pans where there is standing water.

Finding the moisture supply and eliminating it is the way to get rid of any type of household mold.

What kind of mold grows in the window air conditionersWhy do window air conditioners get mold?

1. They have standing water inside the housing.

Standing water means contaminated water. A dark area with standing contaminated water are the perfect recipe for mold production.

Condensation from the air conditioner is meant a drip out of the air conditioner through the back.

How to prevent mold in a window AC unit?

If there is standing water It can only mean that there is something blocking the condensation water from leaving out the back of the air conditioner.

If that’s the case you’re going to have to take the air conditioner out, take the housing off and clean up any debris that is causing the air conditioner condensation not to drip out
of the air conditioner.

This includes getting the debris out of the inside of the air conditioner and anything on the outside that is causing the condensation water not to drip out or the back of the air conditioner.

Another point to make is that there is really no way for that kind of debris to get into the back of the air conditioner unless it is directly under a tree or some other type of rotting wood, branches, leaves, so forth that are able to work their way down into the filter slots on top and sides of the machine.

Cleaning around the air conditioner and making sure that it is not located in an area where anything can get in and stopped up the drip hole also has a part.

At this juncture, Since the air conditioner is already apart and you have identify the problem is being a stopped up drip hole,
Another thing you can do is drill a couple of new drip holes in the bottom of the air conditioner.

It is very easy to do and it will not do anything to diminish the performance of the air conditioner and it will only help keep the condensation from gathering inside the bottom of the machine.

Simply with at least a 3/8 inch drill bit, drill through the bottom of the air conditioning housing. This will add an additional opening in the bottom of the air conditioner for condensation to drip through.

2.  Putting the filters back in when they’re wet.

When the air conditioner doesn’t seem like it’s cooling very well, the first thing to do try used to remove the filter from the front of the machine pointing into the house,  and wash it.

When air can’t get through the filter, it can’t get into your house.

But when washing the filter with water it is important to remember to let the filter completely dry.

Putting the filter back in wet get you back to the fundamental ingredients of mold spore production. Water and darkness.

3.  Improper storage

If you are storing the air conditioner, remember to place it somewhere where it does not have a way to get water in it or cover it well with plastic wrap so that the insides cannot get wet.

Window air conditioners air made to keep mold out. And in fact air conditioning is usually one of the major factors in having dry air.

Dehumidifiers basically function the same way as a window air conditioner and are made for reducing moisture and humidity.

So if you have a problem with mold in your window air conditioner,

Swamp coolers with mold

Evaporative coolers or swamp coolers also have some of the same problems with mold production.

The only thing is that they require water to be circulating inside the machine to be able to blow cool air inside of the window.

A couple of reasons why your swamp cooler may be getting mold is:

1. Allowing the water to stand inside the housing when the unit is not in use.

The water supply continues to drip when it is turned off thereby supplying water to the swamp cooler that it’s turned off.

The main point in keeping mold from getting into the swamp cooler is to keep everything inside the cooler clean.

When you’re not using it, do not allow any standing water inside of the unit and make sure that the pads are dry. Make sure the water is turned off well and is not allowing for any drippage into the pads.

Storing the swamp cooler or getting it ready for winter is an important part of using an evaporative cooler and keeping it free of mold.

The machine must be completely drained and allowed to dry as well as the pads.

Completely disconnect the water ,and use a rain and snow proof cover to completely surround the unit so it stays dry.

Also don’t forget to put the drain plug back in, verman love to find a swamp cooler that hasn’t been put away properly to make their bed in. The drain plug is just the right size for mice and rats to make a front door.


Window air conditioners do not typically get mold because they are built to expel mold, but in some cases usually due to condensation not being able to exit the machine properly they can get a variety of molds including fusarium, acremonium, alternaria, and muscor.

Usually the answer is to figure out why the condensation water is gathering in the air conditioner and eliminate the blockage.

Published by

Dennis Reed

Dennis Reed Owner and Author @ BreatheBetterAir.org