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Air Conditioner Smells Bad

Why Does My Air Conditioner Smell Bad?

Have you recently turned on your air conditioner only to find your house smelling foul a few minutes later?

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Causes Of Air Conditioner Odors

There are several popular causes of your air conditioner putting off foul odors. Some of the most common reasons include:

  • Mold formulating in duct work
  • Mold growing on evaporator coils
  • Clogged condensate lines

air conditioner smells bad, mold image

Mold Growing In Duct Work

Did you know that the duct work in your home is actually a perfect place for mold to grow in the summer?

Mold thrives in cool, damp and dark areas and this is can be a prime description of a lot of duct work.

As the warm air passes over the cool evaporator coils, condensation begins to occur and this moisture, mixed with other dirt and debris can travel through your duct work making it a breeding ground for mold and mildew.

This is a great reason to have your duct work cleaned every few years (not to mention your furnace will thank you for it as well).

Also, to help cut down on bacteria and other contaminates growing in your duct work, check out getting a UV Light installed, such as the APCO Fresh-Aire UV.

Mold Growing On Evaporator Coil

As previously stated, mold thrives in cool, damp environments. Unfortunately, your evaporator coil is both cool and damp.

This cool piece of equipment actually sits on top of your furnace and is usually hidden by a sheet metal type of box.

The evaporator coil’s job is to cool down the warm air that is blown over it (hence cooling your home!).

Over time, the evaporator coil can become extremely dirty from the constant air blown over it.

If you haven’t changed your filter in a long time, this is a great reason why it should be changed regularly.

Imagine air being blow over a metal box that is covered in moisture and dirt (hair, skin cells ect), this is pretty much what you might be smelling!

Not to mention, if you have indoor allergies, this could make the indoors quite miserable for you.

It is generally a good idea to get this cleaned every few years to keep it in top working order as well as save your home from smelling a bit off.

There is a certain process that should be followed when cleaning your coil though so don’t get any ideas and try rigging something up as you might do more damage than good, always give a professional HVAC company a call to have this done.

Clogged Condensate Lines

These lines work hand in hand with the evaporator coil we just talked about.

Below your evaporator coil is a condensate pan that catches any condensation that may fall off of the evaporator coil while it is cooling your home.

The condensate lines then carry this water to a drain (usually in your floor) and then out of your house.

Sometimes these lines can become clogged with mildew or other debris and cause quite the mess to say the least (picture a waterfall coming down over your furnace).

Condensate lines should be cleaned out regularly.

This process is always included in our HVAC Maintenance when getting your AC ready for the summer. 

Clogged condensate lines lead to standing water, which leads to mold growth, which leads to bad odors.

Dirty Furnace Filter

Your air conditioner uses the same filter that your furnace does, so the bad odor your may be smelling may be nothing more than a dirty filter that needs changed.

If you have pets in the home, it’s best to check your filter every month to verify it’s not restricting too much air flow.

Combine a dirty filter with a water leak and you could be smelling a filter that smells like a dirty, wet dog.


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