A Smell Coming From My Portable Home Air Conditioner

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Maintaining a portable air conditioner doesn't end when you pull it out of storage each year.

Portable air conditioners are convenient and, for the most part, trouble-free. You can easily forget that these units do require some cleaning and maintenance from time to time in order to function efficiently. A dirty air conditioner can develop foul odors which can lead to inefficiency and potential health problems for you and your family.

Portable air conditioners come in several types, including:

  • Portable indoor units that sit on the floor and are vented via tubing mounted in a window or through a wall.
  • Window-mounted units that sit within a window opening.
  • Wall-mounted units, which are basically the same as window units, but are instead mounted in an opening in a wall.
A portable indoor air conditioner vents through a hose mounted in a window or side wall.

All smells emanating from any air conditioner have the same cause: mildew or other molds; bacteria growing inside the air conditioner parts, or simple dust particles stirred up in the air. Eliminating these causes of odors is simply a matter of finding where the offensive substances are located and cleaning them away.

It should be noted that permanent air conditioning systems have the same parts and are subject to the same odors with the same causes. With permanent, whole-house units, odors are also eliminated by finding and cleaning the parts where molds, bacteria, or dust accumulates.

Many Odors are Caused by Bacteria and Molds

Most foul smells in a portable air conditioner are caused by bacterial growth or by mold and mildew growth. This is because air conditioners perform their function by removing moisture from the air, and as this moisture condenses inside the mechanism it provides a perfect growth environment for various types of mold and bacteria. The unit's various components can become dirty and moist, providing the perfect environment for bacteria or fungus to thrive.

Smells range from a mild musty odor often related to mildew, to a rotten or spoiled food smell that indicates mold or bacteria growth. Without proper maintenance of the filters, coils, and drains, a portable air conditioner can become overrun with mold, but it is easily cleaned away in most cases. Monthly cleaning or replacement of these parts prevents the odor from returning.

The key to eliminating odors is to find where the bacteria or mold infestation is located. There are three prime targets: the filter, the drain line, and the evaporator coil.


Your air conditioner's filter is designed to trap dust and other small particles and prevent these contaminants from entering other parts, such as the coils and drain line. When too much of this debris accumulates, an unpleasant odor can develop. Sometimes this is due to the debris trapping and fostering mold or bacteria, and sometimes it's because the dust itself begins to circulate in the air. Dirty filters also block airflow and reduce your air conditioner's efficiency.

Filters are easily cleaned or replaced, depending on the air conditioner model. If you have a reusable filter, remove the front cover from the unit and take the filter out. Gently clean the filter with household detergent or with vinegar and water to kill any mold and mildew and to clear the dust and dirt away. Rinse thoroughly and let the filter dry completely before putting it back in place.

Clean or replace your air conditioner filter once each month to prevent odors from returning. If you use the air conditioner daily or have pets, you may need to clean it more frequently.

Drain Line

Dirty filters can also result in mold and bacteria forming inside your air conditioner's drain, which can result in odors coming from the appliance. To remedy this, remove the drain line— which is usually a plastic tube on the side of the unit facing outside—and flush with a mixture of three parts water to one part bleach. This will kill mold or bacteria growing inside and also clear away any debris that might be clogging the drain line. Allow the drain line to dry before reattaching it. If your air conditioner also has a drip pan, this should be pulled out and cleaned each month as well.

Components of a window air conditioner.

Evaporator Coil

Mold or bacteria growing in the evaporator coil can also result in a bad-smelling air conditioner. The evaporator coils can usually be accessed by removing the top of the unit, or sometimes by removing the entire outer casing. Appliance parts stores sell sprays that will kill mold and bacteria and prevent smells from developing. Before spraying the coils though, shine a flashlight inside and look for debris, which can also cause mold and mildew growth. Remove anything large enough to pick out, such as leaves, and wipe the entire area with a wet cloth. If you see mildew or mold growth, use a mild household detergent to clean it away and rinse with water. Leave your air conditioner to dry completely before replacing the top and turning it on.


Renee Miller

Renee Miller began writing professionally in 2008, contributing to websites and the "Community Press" newspaper. She is co-founder of On Fiction Writing, a website for writers. Miller holds a diploma in social services from Clarke College in Belleville, Ontario.