LS Aircon Servicing Singapore

Aircon Smells Bad

Why My Aircon Smells Bad and How to Fix it

If your aircon smells bad, it is a cause of continuous discomfort. Nothing disrupts indoor comfort like a foul odor from your aircon unit. A bad smell indicates potential issues within the system and affects the quality of air you breathe. This comprehensive guide delves into the reasons behind your aircon’s unpleasant odor and provides practical solutions to eliminate the smell and restore fresh, clean air to your space.

Understanding the Reasons for Aircon Smells Bad

Mold and Mildew Growth

One of the most common reasons for a foul smell in aircon is the growth of mold and mildew. These microscopic organisms thrive in dark, damp environments, such as the interior of your aircon unit or the ductwork, especially if there’s excess moisture present.

Clogged or Dirty Filters 

Over time, air filters can become clogged with dust, dirt, and debris. When these contaminants accumulate, they reduce the efficiency of your aircon and create a breeding ground for bacteria and mold, leading to unpleasant odors.

Stagnant Water 

If water accumulates and stays within the aircon unit or drainage system due to improper drainage or leaks, it can promote bacterial growth, resulting in your aircon smelling musty.

Refrigerant Leaks 

In rare cases, refrigerant leaks can occur within the aircon system. Refrigerant mixed with air moisture can produce a chemical odor similar to nail polish remover or a sweet smell, indicating a potential leak that requires immediate attention.

Dirty Evaporator Coils or Ductwork 

Accumulating dirt, dust, or debris on the evaporator coils or inside the ductwork can contribute to bad odors circulating through the aircon system and into your living space.

Why My Aircon Smells Bad

Identifying the Specific Odor

Before attempting to fix the aircon smells bad air, it’s essential to identify the specific type of odor emanating from your aircon. Common odors and their potential causes include:

  • Musty or Mildew Odor: Indicates mold or mildew growth within the aircon unit, ducts, or filters.
  • Rotten Egg or Sulphuric Odor: If your aircon smells bad and smells like rotten eggs, it could be due to a dead animal or microbial growth in the drainage system.
  • Chemical or Sweet Odor: Indicates a potential refrigerant leak requiring immediate professional attention.
  • Dirty Socks Odor is often caused by bacteria and mold growth on dirty evaporator coils or stagnant water within the system.

Fixing the Bad Odor Issue

Aircon Servicing Singapore recommends the following steps to fix the issue if your aircon smells bad air. 

Regular Maintenance and Cleaning 

The most effective way to prevent and eliminate bad odors is through regular maintenance and cleaning of your aircon system. This includes cleaning or replacing air filters, cleaning evaporator coils, and ensuring proper drainage and ventilation.

Cleaning Air Filters 

Dirty or clogged air filters can contribute to bad odors and reduced airflow. Clean or replace air filters according to the manufacturer’s recommendations, typically every 1-3 months, to maintain optimal air quality and prevent odors.

Cleaning Evaporator Coils

Over time, evaporator coils can accumulate dirt and mold, leading to unpleasant odors. Schedule professional coil cleaning as part of your regular maintenance routine to ensure clean and efficient operation.

Checking and Clearing Drainage System 

Inspect the condensate drain and drainage system for clogs or blockages. Clear any debris or buildup to ensure proper drainage and prevent suspended water that can lead to mold growth and odors.

Addressing Refrigerant Leaks 

If you detect a chemical or sweet odor resembling refrigerant, it’s crucial to contact a qualified HVAC technician immediately. Refrigerant leaks pose health risks and require professional repair to prevent further damage to the system.

Fix Aircon Smells Bad

Removing Mold and Mildew 

If mold or mildew is present, use a mild detergent or vinegar solution to clean affected areas. Ensure thorough drying and ventilation to prevent future growth.

Professional Inspection and Maintenance

For persistent or severe odor issues, seek professional inspection and maintenance services. HVAC technicians can identify underlying issues, clean and sanitize the system, and recommend preventive measures to avoid future odor problems.

Preventing Future Odor Issues

  • Regular Maintenance Schedule: Establish a regular maintenance schedule for your aircon system, including cleaning filters, coils, and drainage components. This proactive approach helps prevent odor issues and ensures optimal performance.
  • Proper Ventilation: Maintain adequate ventilation in your home or office to promote air circulation and prevent moisture buildup, which can contribute to mold growth and odors.
  • Monitor Humidity Levels: Use a dehumidifier or air purifier to control indoor humidity levels, especially in humid climates. Keeping humidity in check reduces the risk of mold and mildew growth.
  • Address Water Leaks Promptly: If you notice water leaks or condensation around your aircon unit, address the issue promptly to prevent water damage and mold growth.
  • Professional Inspections: Schedule annual or bi-annual inspections by HVAC professionals to identify and address potential issues before they lead to bad odors or system malfunctions.


If your aircon smells bad, it is unpleasant and indicative of underlying issues that require attention. By understanding the causes of bad odors, identifying specific odors, and implementing appropriate solutions, you can eliminate foul smells and enjoy clean, fresh air in your indoor environment. Prioritize regular maintenance, cleaning, and professional inspections to prevent future odor issues and ensure optimal performance of your aircon system.

Frequently Asked Questions

Q1: Why does my AC smell in dry mode?

It could be mold or mildew, a common occurrence as air conditioners produce water during dehumidification because the aircon acts as a dehumidifier; stagnant water or water might be circulating inside the unit. You’ll likely need to clean the evaporator coil.

Q2: Why does my air conditioner smell so bad?

In brief, inadequate ventilation and dirty coils are common culprits behind a musty smell that develops in the unit over time. Mold or mildew growth inside the unit could also be a contributing factor.

Q3: How long does AC smell last?

When you first turn on your AC, it’s not uncommon to encounter a musty odor for a day or two, which typically dissipates afterward. If you’ve been diligent with your AC maintenance, there’s usually no cause for concern.