Mold On AC Filter! (Causes, Fixes, & More)

By - Ron Singh

Updated -

Air conditioning systems require occasional maintenance, which includes the removal of dirt, replacement of air filters, and fixing of leaks that could cause the growth of mold.

When maintenance is rare, mold will begin covering some surfaces and restrict proper airflow in the long run. 

Mold grows on an AC filter due to constant exposure to moisture that develops when condensation builds on the evaporator coil. Therefore, when mold grows, evaporation goes to the filter.

Why Is There Mold on My AC Filter? 

Mold on AC Filter

There is mold in your AC filter for reasons such as water leakage, high humidity, a spill, dirt mixing up with moisture, or a clogged air filter.

The best way to ensure that mold does not gather in your AC filter is to clean your filter thoroughly when there is a leak or dirt and change your air filter when the need arises. 

In the table below, there are details on the reasons for mold in your AC filter and ways to get rid of the mold:

Is Mold in AC Harmful? 

Mold in an AC harms your health and the HVAC system because it clogs the air filter and produces impure air indoors.

In addition, mold produces a toxic compound or fungi known as mycotoxin, which can lead to various diseases and death in humans and animals when inhaled or absorbed. 

When mold is in your AC, you will inhale some microscopic mold particles. It could irritate your airway and lungs and cause allergic reactions that could be life-threatening if you do not get help on time.

Inhalation of mold should not be taken lightly as several illnesses could result.

These include sneezing, coughing, bronchitis, pneumonia, asthma attacks or rashes, and hives from allergic reactions. 

If mold is unchecked and allowed to grow uncontrollably throughout your HVAC system, it could spread through the entire house and clog your air filters or damage your HVAC system.

When mold growth becomes a full-blown infestation, you will need a professional to examine it and determine whether your HVAC system is due for a change.

How Do I Know There’s Mold in My AC? 

A few telltales signify the presence of mold in your AC, such as a musty or mildew smell indoors while the AC is working.

In addition, black dust around your AC vents, experiencing coughing or sneezing due to stuffy air indoors, or finding mold growing out of the AC unit. 

It is very discomforting to find mold in your AC unit, but if you have been noticing that the air indoors is stuffy and uncomfortable, look at the following signs to confirm whether mold is growing in your AC; 

#1. A Discomforting Musty Smell

 One of the first noticeable signs of mold growth in an AC unit is the musty or mildew smell that fills the house.

To be sure that it is coming from the AC unit, turn it off for a while, then turn it back on, and if the musty smell intensifies, it confirms the presence of mold. 

#2. Sighting Visible Signs of Mold Growth

 The growth of mold might be hard to notice in the early stages, but it multiplies quickly.

Also, you can see the black or orange colors of the mold around your AC unit that resembles accumulated dust if you inspect it closely. 

#3. Frequent Respiratory Discomfort

 If you have been coughing, sneezing, suffering from a runny nose, or any other respiratory illness symptoms resulting from stuffy air indoors while your AC unit is on, then you need to get rid of the mold in your AC unit as soon as possible. 

#4. Streaks of Stains on Air Duct

 If there are no visible signs on the outside of the AC unit yet, you can use a flashlight to check the air ducts and filters for streaks of black, brown, or greenish stains.

Even if they appear faint, if they have a musty smell and stick tightly to the air ducts, it indicates that there is mold in your AC unit. 

#5. Hiring a Professional for an Inspection

The methods discussed above have a 50 – 70% chance of being accurate.

However, hiring a professional to come around and inspect your AC unit is 100% accurate. Professionals will perform a standard mold test and prefer solutions to get rid of the mold if it is found. 

Six Ways to Prevent Mold Accumulation on AC Filter 

You can prevent mold accumulation on your AC filter from reoccurring by ensuring the AC ducts are dry.

In addition, avoid clogged air filters by cleaning them out frequently, fixing AC leaks as soon as you detect them, and replacing air filters when they arise. 

Mold accumulation on your AC filter is dangerous to your health and threatens the efficiency of your HVAC system.

However, with the tips provided below, you can prevent its growth and the potential damage; 

#1. Avoid Moisture in Air ducts

 Mold is known to thrive on moisture in your air ducts or air filter, which could spring from a spill or a leakage.

Therefore, ensure that your air ducts are cleaned occasionally and kept dry to prevent mold growth

#2. Clean Air Filter And Ducts with Disinfectant

 Ensure that you use a safe disinfectant for HVAC systems to thoroughly clean your AC ducts and air filters to kill all bacteria and fungi lurking around them.

#3. Replace Air Filters on Time

You should avoid leaving your air filter screwed in the past the given time as this would only cause dirt to accumulate, clog the filter and cause mold growth in the air filter.

Instead, ensure to replace your air filters within one to six months, depending on the thickness, size, and MERV range. 

#4. Keep the Drain Pans Clean

 The drain pans in your HVAC system can gather unwanted moisture when not appropriately sloped, which triggers mold growth.

To avoid this, ensure you readjust your drain pans and dry them properly. 

#5. Use An HVAC Mold Inhibitor

 Mold inhibitors tagged as HVAC approved should be applied to your air filter and AC ducts to prevent the growth and accumulation of mold.

You should avoid using natural mold inhibitors to spray your AC unit without contacting a professional, as they might not be safe for the HVAC system. 

#6. Monitor the Air Intakes

Air intakes are located at different parts of your AC to allow external air to pass through or expel debris or dirt out of the AC unit.

An air intake facing a dumpster, a pile of dirt, or a contaminated area tends to take in bacteria and fungi that can grow into the mold when moisture touches them. 

To avoid breeding mold through the air intakes, remove waste baskets and other contaminated materials from the places where air enters. 

How to Remove Mold from an AC?

To remove mold from your AC unit, you would need to turn off the AC unit and unplug it from the power source, wear protective gear, disassemble the AC unit, the right clean the air filter, scrub the mold thoroughly and allow all the parts dry before reinstalling the parts. 

Experiencing a mold infestation in your AC unit is hard to handle without proper guidance on ways to get rid of it.

However, with the step-by-step guide provided below, you can easily remove mold from your AC unit; 

#1. Take the AC Unit Apart

Begin by turning off the AC unit, unplugging it from the power socket, and disassembling it.

Make sure you have a safety Google on and a nose mask before diving into this mold removal process.

#2. Clean the AC

 Vacuum the dust surrounding the AC unit and use an HVAC-approved disinfectant to clean the filter thoroughly; if it is reusable and not, replace the filter.

Next, apply a cleaning solution and allow it to soak for 10 minutes, then scrub the mold out of the  AC unit carefully. 

#3. Dry the Parts And Reinstall

 After scrubbing, allow the parts to dry appropriately before screwing them back together, and ensure to use a new air filter if the old one was not reusable. 

Final Thoughts

The growth of mold in an AC filter is a prevalent and recurring problem that households with air conditioners face.

Mold results from moisture, accumulated dirt, or clothed air filters. It is also dangerous to respiratory health and the HVAC system. However, proper maintenance can fix it and prevent its recurrence.

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