Air Con Smells Musty

Air Con Smells Musty

Have you experienced coming to work, ready to start a productive day, but suddenly noticed a faint odor as you entered the room and realized the air con smells musty? If yes, then this must have affected your workday because you keep noticing the unpleasant smell.

Air Con Smells Musty

Have you ever experienced coming home ready to shower and relax after a long day’s work; you switch on your air conditioner and about to go on your routine but you smelled something unusual then realized your air con smells musty? Even tried cleaning around the place, and spraying air freshener, yet your effort is ineffective because still, the air con smells musty. Adjusting the thermostat does not help in getting rid of the smell, too.

If you have been in both situations asked above, then you have experienced what many other home and business owners experienced. If you have not, then good for you because you are about to know  what you can do to avoid it from happening.


Possible Causes Why Air Con Smells Musty

Before giving you the tips to prevent such from happening, we must know the source first. We must look over the possible reasons why air con smells musty. We will also try to explain the causes why the air conditioner smells musty after winter and the air conditioner smell of burning.

An unpleasant smell coming out of your air conditioner is a sign that something is wrong. Unless you use scented fresheners, the air that comes out of the unit isn’t meant to have a smell. 

  • Molds

Air Con Smells Musty

Due to humid weather, excess moisture builds up inside the air conditioning system. If it does not drain properly, this may result in mold spreading in the ductworks. Keep in mind that molds need these four things to grow: 

  1. Warm temperature 
  2. Absence of light
  3. Organic matter (like wood or dust) to grow on
  4. Moisture for their nutrients. Excess moisture may also be attributed to water leaks within the AC system.

Increased risk of respiratory problems can be caused by exposure to mold. Black molds may be toxic and you need to get rid of them immediately.

  • Drip Pan (Drain Pan) Is Clogged

Air Con Smells Musty

Drip pans also called drain pans or drip tray is an air con component that collects water that drips from the evaporator coil. Water droplets fall into the drip pan because of moisture. Molds build-up when the drip pan is not draining the collected water properly or when it rusts. Drip pans can be bought at hardware stores, just take note of your air conditioner’s make and model.

  • Condensate Line is Blocked

Air Con Smells Musty

Mold can also gather in the condensate line. The part of the air conditioning system outside the house is where the condensate line can be found, beside the condenser unit. The function of the condensate line, sometimes called the drip line, is to drain the collected water by the drip pan. It helps remove condensation produced by the coils. This is a PVC pipe with a small diameter which can be a perfect place for molds to grow and clog the line. If the drip line clogs, water and dirt will get stuck in the drip pan, causing more mold to grow.

So when your air con smells musty, you might need to check the condensate line and make sure it is draining away water properly. If it drains colored water or sludgy liquid, then the line must be blocked. For ductless units indoors, a visible sign is water leaking down on walls.

  • Moisture in Filters

Air Con Smells Musty

Clogged condensate line or drip pan or anything that keeps water from draining causes the air con filter to soak up moisture. The filter’s function is to keep the AC system free from dust and dirt. If you do not change filters regularly, dirt lodges in the filter, so when the filter is exposed to moisture, it accumulates molds, too. Therefore, blocking the clean flow of air. This may pose health issues to you.

  • Muck in Evaporator Coil

Air Con Smells Musty

The evaporator coil’s function is to absorb heat inside the room. These contain coolant, are made of copper and conduct heat and are located on the internal part of the AC unit. The dirt can pile up instead in the evaporator coil when the air filter is clogged. Blocked airflow because of dirty filters also results in moisture accumulating on evaporator coils. And when moisture builds up on the coil while the refrigerant continues to cool air, these water droplets will freeze on coils. This dirt and frozen water droplets thus make air con smells musty. 

Other Causes Why Air Con Smells Odd

  • AC Unit Isn’t the Right Size

Air Con Smells Musty

If the air gets cycled around the area fast, the air is not possibly dehumidified entirely. This will result in excess moisture in the system. This happens when an air con unit is too big for the area. AC unit size is computed based on your area measurement, ceiling height, type of insulation, and the number of persons staying in the area.

  • Dead Insects 

Air Con Smells Musty

Insects and rodents tend to take shelter in the duct system. Unfortunately, some of them get trapped and dies in the ductworks, producing that distinct bad smell.

  • Chemical Leaks

Another reason for strange smells coming out of your AC unit is the possibility of a chemical leak. Immediately turn the unit off if you noticed that a chemical or gas-like smell (a bit different from the air conditioner smell of burning) is emitting from the air con. Open the windows to provide natural ventilation around the area. Then, have the unit checked by a technician.


Air Con Smells Musty, How Do I Avoid It?

Possible reasons for why air con smells musty and strange are suggested above. Knowing those, you probably want to try to avoid it. Here are the things you can do:

  • Check for any signs of water leak in the ducts. If there are any, repair these as soon as possible to prevent molds. 

  • If there is already a mold build-up, have it cleaned. Having a dehumidifier is also helpful in keeping the molds from growing.

  • If you see signs of a clogged condensate line, clean it with water and bleach solution. You can also clean it by pouring distilled white vinegar around 1 cup amount in the line and rinse with water after half an hour before turning the air con on. Do this once a month.

  • Change the air con’s filter every 2 months. If you own a pet or have allergies, every month filter change is advisable.

Air Con Smells Musty

  • You can use foaming coil cleaner in removing dirt and moisture build-up in the evaporator coil. But deep cleaning of coils is a task best done by the experts.

  • If you are to clean the air conditioner by yourself, please do so without endangering yourself and without damaging the air-con. 

Air Con Smells Musty

  • Do not try to use air fresheners and the likes to cover up the bad smell coming from the air con. Doing so may just be temporary and likely not help. It is better to target the main cause of the problem and have your AC system checked.

Air Con Smells Musty

  • So you won’t have to worry when your air con smells musty, call an HVAC technician to have your air con checked including its ductworks. They have the expertise and know-how to handle the problem that will help you prevent it from happening again.

Air Con Smells Musty

  • Check the years that the air con has been functioning. You may consider buying a new one if it is more cost-efficient instead of wasting time and money having it repaired now and then.

D-I-Y Steps in Cleaning an AC Unit

Air con technicians may not always be available. They may not adjust to your schedule. If so, you insist on doing the cleaning by yourself, here are some of the basic steps for cleaning AC units:

  1. Make sure to switch off the main power supply to the air conditioning unit.
Air Con Smells Musty

Remove the external part cautiously, this includes the compressor and coil. Put it in a place where it is not exposed to more dirt in the process of cleaning.


3. It is best to have compressed air blown from a distance to prevent damages to internal AC parts.

4. Manually clean the front and back parts of the AC from dust particles. Use a clean cloth or a small brush.

5. Use a cleaning solution to clean the duct and vent cautiously. Then rinse the solution with water.

6. Get rid of dust and dirt collected on the drip pan by flushing. Avoid applying too much pressure.

7. Wipe the unit using a clean dry cloth. Let the unit dry for a few hours.

8. If the unit has fully dried, reassemble it.  

Take note that it is best to follow the cleaning instructions included in the air conditioning unit manual. Make sure to use the appropriate tools for cleaning. In addition, the air conditioner has components that can cause electrical shock. If you are not confident in dealing with the electrical it may be best to leave it to the experts.


Air Conditioner Smells Musty After Winter

Air conditioner, previously considered as a luxury in homes, has now become a necessity in some places, especially in tropical countries where heat indices can rise high to dangerous levels. However, it cannot be said the same for those countries not in the tropic zone because they experience winter – the season when people uses heater instead of air con.

Lack of use of the unit can be the reason why the air conditioner smells musty after winter. It is best to clean the AC unit before the winter season – before you stop using it for a long period. Then clean it again before using it after the winter season. In this way, you will get rid of moisture and dirt that gathered inside the air con during the time it was not in use.


Potential Causes of Air Conditioner Smell of Burning

  • Dust from Non-Use of Air Con. Dust accumulates in the air conditioning unit if it is not used for a long time. When turned on, after lack of use for a long duration, these specks of dust burn and release a bad smell. If this is the problem, the smell will only be temporary. But if the air conditioner smell of burning does not dissipate, you might want to check some other AC system components.

Air Con Smells Musty

  • Cigarette Smoke. Odor coming from cigarette smoke is absorbed by the air con filter and on the evaporator coil. These tobacco particles in the air filter are blown back to the room when the air con is switched on, which may be the cause of the burning cigarette smell. Regular cleaning and changing of air con filters can get rid of the smell.

  • Electrical Components. If the air conditioner smell of burning continues for about 20 minutes, it might be an electrical issue. This might be a serious problem so turn the AC system off as soon as possible and call a technician.

The air conditioning system consists of several components; most of them are electrical and mechanical, like circuit boards, coils, and motors. The smell of burning indicates signs of mechanical issues or electrical problems. These might be the wiring or compressor. Either way, it might be best to contact HVAC (heating, ventilation, and air conditioning) technician immediately. 

Water and electrical is not a good combination, especially if you have little to no background in handling electrical works and the chance of electrical shock is great. Do not try to fix things yourself since this may worsen the damage or worse, cause injury.  Let the technicians handle these kinds of repairs before running the AC system.


An air conditioner has become a necessity to make our workplace more conducive and our homes more relaxing. No matter the reason, it will not help us to have conducive workplaces and calming quarters if it keeps releasing unpleasant smells.

However, if your air con smells musty, you don’t need to panic because it does not necessarily mean a threat and it might just be a sign that requires tech service. Especially if your air conditioner smells musty after winter, this is not a big deal and you only need to clean your unit before turning it on. 

Components of an AC is a system that should work simultaneously to be efficient, which means that if one component is not functioning properly, other components will be likely affected, too. 

If you noticed any of the possible reasons listed above, remember that there could be one AC component that is not functioning well which also affects other components. If this happens, then the whole system will be affected. On the other hand, regular maintenance and cleaning can save you the problem of air con smells musty.

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