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Why My Air Conditioner Smell Bad?

When you turn on your air conditioner, you expect to be greeted by nice, cool air. However, if the air coming from your AC vent is smelly, you might have a serious problem. Some air conditioner smell are merely irritating while others are hazardous.

This unpleasant air conditioner smell is actually called “dirty sock syndrome” and can be caused by several factors: dirty coils, improperly sized unit, clogged drain, and problem with air filtration system. Most of the time, the main cause of an air conditioner smell is lack of proper cleaning and maintenance. Dirty sock syndrome is caused by mold and mildew buildup in your air conditioner, especially on the evaporator coil.

Dirty Coils

The coils in your air conditioner will collect dust and dirt over time, but dusty coils alone shouldn’t cause air conditioner smell. If mold and bacteria have grown on the coils, you will notice an odor because the air blows directly over the coils as it enters your home.

Improperly sized air conditioner

Everyone knows that an air conditioner is used to cool your home, but many people don’t realize that it also performs a second function: dehumidification. Air conditioner that is too large for a home will perform a cooling cycle quickly, not running long enough to sufficiently remove moisture from the air. On the hot summer days, when humidity builds up, mold and mildew can develop and distribute the unpleasant air conditioner smell throughout the whole house.

Clogged drain

The condensate drain line runs from the coils to the outside of the AC unit. It is designed to catch and drain away condensation that drips off your evaporator coils. But if this system gets clogged, the standing water that’s trapped can quickly lead to mold and bacteria growth.

Air filtration system problem

Your air filtration system removes contaminants from your home’s air. Whole house air cleaners and ultraviolet lights are especially good for removing contaminants that can produce odors in your home. If something is wrong with your air conditioner air filtration system, those contaminants will not be properly removed and your home’s air can begin to smell.

The most important factor in preventing dirty sock syndrome is to make sure that you choose a high-quality air conditioning filter.  Mold, mildew and bacteria need dust and other porous substances to thrive.  Removing these from the air before they get into your coils is one of the key ways to prevent dirty sock syndrome.


Be sure to have regular maintenance performed on your central air conditioner by a licensed HVAC contractor as a preventative measure. If you are having central air conditioner problem and in need of service or replacement call us today at 647-847-2998 or fill out online request form and one of our friendly staff will get in touch with you as soon as possible.

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