5 Reasons Why Your Air Conditioner Smells Musty

 
A black and white image of air conditioner vents in the ceiling of a building
 

Noticing that your air conditioner smells musty? There are a few potential reasons why this is happening, and it shouldn’t be ignored. For information on what’s causing the smell and how to fix it, read on!

Is it an issue when your air conditioner smells musty?

If your air conditioner smells musty, you might be wondering if it’s really all that much of a big deal. How bad can the problem be, really? Will it go away on its own? Is it okay to just ignore it? 

The truth is that it’s a really bad idea to ignore any kind of unusual smells coming from your air conditioner. If your air conditioner smells musty, it indicates a deeper problem that may have been there for a while and that could be serious.

Some of the key problems that could be the reason the air conditioner smells musty are a mold infestation, a blockage, or broken components. All of these problems can escalate if they aren’t dealt with and go from small issues with straightforward solutions to much bigger challenges that cost a lot to fix. So, don’t ignore it if your air conditioner smells musty! Make sure you check to see if any of the reasons below are causing the problem.

Why does the air conditioner smell musty?

These five issues are the most likely reasons why your air conditioner smells musty. All of them are connected to a build-up of dirt and moisture in your ductwork, which is why regularly cleaning your HVAC system is so crucial!

#1 - Dirty filters grow mildew and lead to frozen evaporator coils

Your air conditioner filter is designed to catch the dirt in your air to stop it from being circulated through the system. Naturally, after a few months, the air conditioner filter is full of dirt, and it needs to be either washed or replaced altogether, depending on the type of filter you have. We have a guide on how often to change your air conditioner filter if you’re interested.

If a dirty filter is left too long, it can be the reason your air conditioner smells musty. Moisture - whether from the air itself or from a drainage leak - can end up collecting on the filter and creating the perfect environment for mold and mildew to grow. You’ll start to smell this as air is blown through the dirty filter back out to your home.

 
Water droplets pool inside an air conditioner vent
 

A dirty filter can lead to another problem: when airflow is slowed or obstructed, the warm and humid air in the system can end up depositing dirty water on the evaporator coils, where the AC’s cooling causes it to freeze. Frozen evaporator coils stop the air conditioner from working properly, and the buildup of dirty, frozen water can start to smell.

#2 - Dust build-up on the heating elements

Something else that can mean the air conditioner smells musty is if there is a build-up of dust and dirt on the heating components - turning on heating after a can cause a brief dusty or burning smell as the dust is burnt off. If the burning smell persists, there may be a deeper problem with your furnace or electrical wiring, so call a professional.

#3 - Dirty or blocked drain pan

The drain pan catches the condensed water that your air conditioner strips from the air as it’s cooling. In theory, the water should flow out from the drain pan without growing stagnant, but if the drain pan is old or the drain line becomes clogged, you may start to get standing water. When mold grows in the drain pan, the air conditioner smells musty.

You can empty and clean out your drain pan yourself, or you can get an HVAC expert to give your whole system an assessment and clean everything out - that way, if there’s any mold anywhere else, you can be sure you got it.

#4 - Mold or mildew in the ductwork

If water pools or condensation builds inside the ductwork, it can become the perfect environment for mold to grow. Dark, damp, and dirty, ductwork that hasn’t been cleaned will grow mold - and then spores from the mold will be blown down into your home by the air conditioner’s fan. The build-up of dust, dirt, and mold in the ducts can lead to irritation and allergic reactions in the people who are breathing the air in your home. That’s why your air conditioner smells musty, and that’s also why it’s so important to have your ducts professionally cleaned. 

 
Mold and mildew build-up on an AC vent
 

#5 - Dirty or blocked condensate line

The condenser unit is part of the air conditioner that is outside the home, and the condensate line is a pipe that channels the water from inside the AC out to a storm drain or simply to the ground. The pipe’s small size and proximity to the outdoors means that it is easily clogged with dirt, mud, and bacteria - and these can be the reason why your air conditioner smells musty. It’s important to clean your condensate line every month or two to make sure that water can easily escape from your HVAC system without building up.

Simple solutions for when your air conditioner smells musty

As you can see from reading this article, though there are several different potential reasons why your air conditioner smells musty, they mostly boil down to one main culprit: mold. When mold is allowed to grow, whether it’s in the ductwork or the air filter, it’s going to result in an odd musty smell. If it spreads from the ducts into the flooring or the walls, it can cause significant damage to your home, so it should be treated as soon as possible.

The best way to prevent this from happening, and to treat it if it does, is to get your HVAC system professionally cleaned. Our powerful shop vacs, unique piping tools, and rigorous disinfectant will get rid of any mold or dirt build-up inside your ducts and vents with absolute ease. Get in touch to book a free consultation today!