Why does my air conditioner smell bad?
June 28, 2019
Firstly, we have to determine the type of smell coming from your air-conditioner. The two most common smells we take questions about here at Advanced Clean Air are –
- Musty or “dirty sock” smell, which is usually caused by mould, mildew and bacteria build up from inside your air conditioner. Additionally, dirty filters can also give off a musty smell.
- A rotten egg smell, which usually means there is a dead animal inside your unit. The most common cause of a rotten egg smell is geckos living inside air conditioners where they often die and begin to decompose. That’s why when you turn on your air conditioner, a horrible odour circulates throughout your home.
If you have a musty smell coming from your air conditioner you likely have one of these problems:
- Mould on your evaporator coils
- Mould on your scroll fan and casing
- A clogged drain/condensate line
So how and why does mould grow inside your air conditioners?
As warm air passes over those cold coils (radiator looking thing underneath your filters), condensation occurs. And if there’s any dirt or dust present it provides the perfect breeding grounds for mould, mildew and bacteria. This gunky mix normally loves the damp drain pans of your air conditioner and can grow over the drain outlet causing your air conditioner to leak.
Signs of a dirty evaporator coil and scroll fan:
- Visible signs of dirt, mould/mildew build-up
- Ice forming on coils
- Weaker than normal air flow
If you smell either of these from your air conditioner contact Advanced Clean Air - The Cleanest Air Anywhere to give your air conditioner our deluxe clean and have it back to “like new” in no time.

The first sign many people notice is a musty, mouldy odour. If you do a thorough clean of your office or commercial space and the smell is still there, it’s time to check your vents. Getting your Air Conditioning Contractor to remove the covers and take a quick look inside may confirm the issue, especially if you see mould or notice a stronger smell in that area. If the scent is stronger, but you can’t see the mould, then the growth is possibly further in the ducts. Another sign of a mould issue is the sudden onset of allergy symptoms. If you or a co-worker notices burning eyes, scratchy throat, or a runny nose that gets better when you leave the office, there could be an issue. Arranging for your HVAC technician to check your filters should be the first step. If it needs to be changed they can install a new one. If the symptoms continue they can do a quick check of your vents and a visual check of your ducts. Inspecting your duct work can also provide clues to a possible mould problem. An Air Systems Cleaning Specialist (ASCS) can check for signs of moisture build-up, such as condensation, dark spots, or actual leaks. Mould needs water to grow, so any signs of condensation or leaking could indicate a growth hot spot. Duct cleaning and coating is a specialised job and as such the majority of HVAC companies sub-contract duct cleaning and coating out to companies like ours. At Advanced Air we have our Air Systems Cleaning Specialist on staff ready to undertake any duct inspection, cleaning or coating project you may have.