Across the United States, nearly 250 million people rely on air conditioning systems. However, when our AC or HVAC filter turns yellow, it’s time to switch off the system.
An air conditioner (AC) or HVAC filter usually turns yellow because of yellow mold growths. But the type of air filter (e.g., Colorfil or MERV 13) used in the unit, and clogged filters can also cause an AC filter to turn yellow.
This guide covers all the reasons why an AC filter has turned yellow, including step-by-step instructions on how to fix each problem.
3 Reasons Why Your AC Filter Is Yellow
When one part fails, it causes a cascade of problems that spread from one system to the next.
A yellow AC filter can be caused by a number of other problems, including a clogged filter or even external influences like mold infestations in the home.
Here are the reasons why your AC/HVAC filter yellow:
1. Yellow mold
Yellow Mold is one of the most common reasons for an AC/HVAC filter to turn yellow.
Air conditioners are moisture-rich environments that are perfect for mold growth, especially on the filters.
But there are usually two possible reasons why the moisture has become a problem:
1. Condensation from running the air conditioner can result in a damp evaporator coil, which can carry moisture to the air filter, allowing yellow mold to bloom.
2. If the filter isn’t fitted properly, water can drip or pool around the base of your indoor AC unit. The moisture in your system can then drip directly onto the filter making it damp, providing an ideal home for mold.
Normally it’s best if you notice an increase in moisture around the unit after cleaning or changing the filter to switch off the unit, and remove the filter. Check the filter for any damage or tears and then reinstall it correctly before turning the AC back on.
Types of yellow mold that can grow in an AC filter
- Serpula lacrymans.
- Mucor.
- Epicoccum nigrum
- Aspergillus.
How to tell your AC filter is yellow due to mold:
- Turn off the whole system.
- Access the filter and remove it from the air conditioner.
- Examine the filter’s color. It’s most likely mold if it’s yellow following the wet summer season, but you may see other types of mold, especially brown and black types.
- When checking the filter see if it releases any musty smells. Most mold will give off a musty odor.
- Yellow dust around your air conditioning vents
- Have a qualified AC/HVAC specialist look it over to confirm if it’s mold.
- Sometimes, if there are people allergic to mold around the house, they might start experiencing allergic reactions or asthma attacks when exposed to mold. Mold exposure induces fever and shortness of breath in people with mold allergies.
- Mold exposure can also cause a stuffy nose, red and itchy eyes, coughing, and wheezing.
How to Fix a moldy yellow AC filter:
- If you find mold on your air filter, then throw it out and replace it as quickly as possible. It should not be cleaned and reused.
- If possible find the source of the mold and get your AC system tested to make sure that no mold it isn’t growing inside the air handler.
- Hire a technician to clean your filter and the affected areas.
- Purchase an air purifier that can remove mold and its spores.
How to prevent mold growth in your AC system
- Install an air cleaner or purifier to capture and destroy mold and its spores from the air to avoid infestations – Here Are 7 Great Examples.
- Maintaining and cleaning your AC/HVAC system on a regular basis will stop mold from establishing in the first place.
- To keep mold spores out, use an air filter with a MERV 13 rating.
- Clean and replace your AC filters according to the manufacturer’s instructions.
Read more about how to stop your AC filter from getting wet here.
2. Filter type
The type of AC/HVAC filters can actually be the reason why it is yellow.
MERV 13 AC filters can be yellow when first purchased. This is their correct color, and is nothing to be concerned about.
While other types of air conditioner filters turn yellow when it is time to have them replaced.
A great example of these are the Colorfil filters.
Colorfil filters are AC/HVAC filters that filter pollutants, allergens, and odors from indoor air. T
Normally, while still new, the colorfil filters are a vibrant pink or purple in color. But after a period of use, they change from the pink or purple color to yellow to let you know that they are nearing the end of their capacity.
This is to prepare you to purchase replacement filters.
The colorfil filters need to be replaced every 4 months or earlier in dusty environments. Poor indoor air quality, the season, and the thermostat settings determine how fast colorfil filters will change to yellow and need replacement.
How to tell colorfil filters require replacement
- Turn off the air conditioning system.
- Access the filter location.
- Are there changes in the color of the colorfil filter to yellow? If yes, it is nearly used up (0-25% capacity remaining) and needs replacement soon.
- Double-check if it is clogged with dirt, dust, pet fur, or hair.
- If there is dust around the air vents it is dirty.
- Reduced air flow is another sign that filters need to be replaced.
- It also has to be replaced if there are signs of dust and debris on it.
- Have you noticed that your cooling system isn’t working as well as it used to? It means the filters need to be replaced.
Solutions
- Replacing the filters as specified and on time.
- Schedule a regular maintenance routine and follow it.
3. Clogged filters
Clogged filters is the most normal reason for AC and HVAC filters to appear yellow. Even though there are different types of AC filters, all of them become clogged after a certain amount of use.
This is how they are designed. Over time the contaminant capturing capacity of the filter is simply used up.
Some last one month, others three, and others even up to 12 months. However, the lifespan of a specific AC filter is not certain, because even the filters meant by the manufacturers to last 3 months will last less time in dusty environments.
While many things clog an AC filters, including dust, dirt, hair, and mold.
The air conditioner filter usually turns yellow if they get clogged with dust. Especially since a lot of the dust in our homes is actually dead skin cells.
How to tell if the AC filter is clogged
Before even accessing the AC filter, some initial signs of a clogged AC filter include;
- Increased electricity costs.
- Poor indoor air quality.
- Build-up on blower fans and ductwork.
- Dust near air vents.
- Disrupted air flow.
If you notice the above signs, check the filter condition to see if it needs replacing. To do so;
- Turn off the entire AC/HVAC system.
- Open the filter compartment and access the filter.
- If it’s clogged, you’ll see debris settled on it.
- You’ll likely also notice the color change if the filter is clogged.
Solutions to a clogged AC filter.
- Changing AC filters on a regular basis and as often as is recommended in your user manual.
- Cleaning the AC filters regularly can stop filters from becoming clogged in the first place. They can often be washed, but if not vacuum them or replace them with new ones.
How to replace an AC filter.
- Turn off the entire air conditioning system.
- Locate your filter container and open it.
- Remove the current filter you’re using.
- Look it over carefully to check whether it’s clogged.
- Dispose of the old clogged filter.
- Remove the new filter from its packaging.
- Place the new filter in the proper location.
- Make sure your filter housing area is closed tightly before turning on the system again.
Should air filters ever be yellow?
Air filters are not supposed to be yellow. Usually, a new air filter will be white or off-white in color, but after a period of use, it will start turning to gray, brown, black or yellow due to the accumulation of dirt, dust, or mold.
When it’s completely clogged, it’s best to clean it or replace it with a new air filter. However, filters such as colorfil will turn yellow when it is time for them to be replaced.
What a bad AC filter looks like
A bad AC filter will look dusty, clogged, or discolored. A bad AC filter will change its color from the initial one to a much dull or darker color due to the accumulation of contaminants such as dirt, dust, debris, hair, and fur.
