Why Does My Aircon Smell? 7 Reasons Why & How To Fix

Bad odours from your air conditioning are due to a range of factors, including leakages, electrical faults, a build-up of mould, animal infestations and damage to internal components. These are not only unpleasant, they can also cause health issues including asthma, allergies, skin irritations and respiratory problems. But why is your air conditioning emitting unpleasant smells, and how do you fix it?

A stale smell

Mouldy Split Air Conditioner

A mouldy split system air conditioner

If a stale or musty smell starts emanating from your unit, it is typically due to the build-up of mould or mildew. This occurs naturally as air conditioners are dark and humid places that mould and mildew love to inhabit!

Air conditioners are designed to remove excess moisture from the air while cooling or heating it, however, if moisture and humidity start to build up, problems begin to occur. Filters, tubes and evaporator coils are significant hotspots for growth. In addition to emitting unpleasant smells, mould and mildew can also cause health issues, including worsening respiratory conditions and asthma.

A musty smell

All air conditioners collect moisture as part of their regular operation. When the system is working correctly, moisture is collected in a drip pan and either flows down a drain line or is pumped safely outdoors.

If your unit is leaking an unusually large amount of water, you may start to notice a musty smell, often compared to the smell of dirty socks! Regardless of the cause, the first step is to turn off the unit to prevent further damage to your property.

There are a number of possible reasons your air conditioner is leaking, and most of them will require involving a professional air conditioning technician to solve the problem.

One is due to clogged air filters, as they will restrict the airflow passing over the evaporator coils. They can then ice over, and water can start to drip as they thaw. In the process, the heat pump and compressor may be damaged, which can lead to expensive repairs.

Some units have a condensation pump to push water collected outside. If this is damaged in any way, the water will have no way to escape, it will build up and the system will start to leak. In this case, the pump will need to be repaired or replaced.

Another common reason an air conditioner may start to drip water is because of a clogged drain line. Debris and dust can collect and eventually clog the drain hole, and once the pan is full, the water will start to drip over the sides.

If an air conditioning unit is low on refrigerant, its coils can begin to freeze over. Each time the unit shuts off, the ice will melt, and it can start to overflow the drip pan.

Units that aren’t installed correctly can also lead to leakage over time. This is particularly the case with the P-trap and vent line that are designed to prevent water from being drawn back into the drip pan when airflow causes negative pressure. In addition, if ductwork wasn’t properly sealed and insulated when it was installed, moist ambient air will start to be drawn into the system. Once mixed with the cooler air in your unit’s ducts, condensation can form, and leakage may develop.

A burning smell

Air conditioners have their fair share of circuitry and components. And like all electrical appliances, faults can occur. Burning or “gun powder” odours typically mean functional problems with electrical wires, fans or motors, caused by overheating, water damage, a build-up of dust, or the circuit may be receiving the incorrect voltage.

Over time, electrical components can also wear out, causing mechanical failures and lead to short circuits. If you notice burning odours or even worse, smoke, shut down the unit immediately and contact your air conditioning technician as soon as possible.

An exhaust smell

Air conditioners have motors, and motors require lubrication in the form of oils. If the smell is more like exhaust fumes, it could be due to an oil leak or the central unit overheating, which can cause oils to burn. Exhaust aromas are not only unpleasant, they can also affect indoor air quality and lead to health problems.

A rotten egg smell

The smell of rotten eggs shares many similarities to natural gas. So if you are detecting this odour, your air conditioner may have a gas leak. Gas leaks can lead to carbon monoxide poisoning, which can be extremely dangerous. You should open windows immediately to ventilate the area, shut the unit down, and disconnect your home’s gas at the mains as a precaution. Then call your technician ASAP!

A chemical smell

If your air conditioner is emitting a chemical-like smell similar to chloroform or paint thinner, it may signify your unit is leaking essential fluids. Refrigerant gas in reverse cycle air conditioners treats the air before it is dispersed throughout your home. A chemical smell suggests that the refrigerant is leaking, which can limit your system’s performance as well as be hazardous to your health.

A methane smell

Methane Smell Dead Animals

Dead animals can give off a methane smell

A methane or sulfuric odour can indicate an animal (like a mouse, rat, bird or possum) has taken shelter in your air conditioning system’s ducts and has died. This is particularly the case during winter when animals are seeking a warmer place to nest. However, dead animals not only cause foul odours. They can also chew through and damage ducts, wiring and components.

How to eliminate smells

If you’re wondering how to stop aircon from smelling, the most obvious answer is to have your unit regularly serviced. Although some maintenance can be done yourself (cleaning filters, for example), other servicing should be done by a licensed air conditioning technician.

They will keep your unit running efficiently, ensure indoor air quality and address any issues (including bad odours!) before they become more significant problems. Typically, during a service they will:

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