Internal component of split system air conditioner installed on wall. Underneath it reads AIR CON SMELL. Toxic looking smoke covers the image, indicating bad smell coming from unit.

5 Common Air Conditioning Smells and their Surprising Causes

Noticed some funny air conditioning smells coming from your split system or ducted unit? These smells could indicate a variety of possibilities, from bacterial growth build-up to fried circuits.

It may also simply indicate that your filters need to be cleaned or replaced. Whatever the situation, a smell produced by an air conditioner could be a sign of a severe problem that needs prompt investigation.

So, if you turn on the air conditioner and a bad smell emanates from the vents, or from the internal or external unit of your split system, then you’re going to need to request maintenance.

Here are five of the most common air conditioning system smells and their causes.

air conditioning smells like mould

1. Mildew or Mould Air Conditioner Smells

If your air conditioner emits a stale or musty aroma around the house, it could result from a leak somewhere in the system.

It’s not uncommon for the drip lines, drain pan or evaporator coil to clog and then leak. This leaking water can pool and become a suitable breeding ground for mildew or mould – two of the more common causes of bad air conditioner smells.

Alternatively, a musty smell can be caused by a dirty air filter, particularly in regions with high humidity. The additional moisture from your air conditioning unit can settle on the filters and produce unpleasant smells, while dirty filters can also affect air quality.

So, we recommend that you clean the filters every three months, whether or not your air conditioner smells bad. Anyone can clean a dirty filter. However, you will need the assistance of an expert to fix a leak.

burning smell from air conditioner

2. Air Conditioner Creates A Burning Smell

Air conditioning carries its fair share of components and circuitry. And like all electrical appliances, there’s room for faults. A burning odour will likely indicate that one or more of the electrical components has fried. This can be caused by water damage, overheating, a build-up of dust and many other issues.

If the smell dissipates quickly, then there may be nothing to worry about. But if the smell sticks around for longer than a few seconds, or the unit produces smoke, you should shut it down immediately and call a heating, ventilation and air conditioning (HVAC) technician before further use.

Scheduling maintenance for your air conditioner can reduce the likelihood of build-up and clogs, so it’s always wise to organise an annual service.

Similarly, a burning smell in the aircon unit could indicate that the fan motor or circuit board has burnt out and needs replacing. This bad air conditioner smell can be caused by overheating, water damage or the circuits receiving the incorrect voltage.

3. Air Conditioning Produces a Cold-Like Coolant Smell

An air conditioner emitting a cold-like coolant smell can indicate that your system is leaking essential fluids. Refrigerant gas is present in reverse cycle air conditioning. The system relies upon this gas to treat the air before it’s dispersed throughout your home.

This odour suggests that the refrigerant is leaking. It has the potential to exacerbate existing health problems while also limiting the performance of your air con.

Only licensed air conditioning technicians are legally permitted to perform an air con regas. So, if you do smell this odour, shut down your AC, open the windows and give us a call.

4. AC Smells like Exhaust Fumes

Air conditioners have motors, which require lubrication to keep functioning at their best. Therefore, oils come into play.

If the oil was to leak, or the central unit was to overheat, it’s possible for that oil to burn and for those undesirable exhaust fumes to affect the indoor air quality.

If your home is not ventilated properly, the exhaust may cause problems beyond just an unpleasant smell. So, contact your HVAC system professional and get that issue fixed.


air conditioning sulphur smell

5. Aircon Produces Rotten Smell

We saved the “best” for last. If you’re trying to enjoy the comfort provided by an air conditioning system only to be struck by a highly unpleasant, rotting odour, then there’s a good chance that an animal or rodent has died in your system.

Critters like rats, mice, lizards, birds and possums have all been known to explore the insides of a compressor or ducts only to get trapped within and die. It’s only a matter of days before they start to produce a distinct smell and you’ll find your air conditioner smells terrible.

The good news is that our technicians can address this problem and investigate if the system’s performance has been affected.

Air Conditioner Repairs

If you’re experiencing any of the above air conditioning smells, your best course of action is to have a professional inspect the HVAC system and recommend the appropriate fix.

Repairs or a thorough clean will hopefully be all that’s required for your air conditioning unit. But if key circuitry has burned out, it might be time to consider replacing the air conditioning system or looking into an upgrade.

Whatever the cause, contact the experts at Metropolitan Air Conditioning, and we can schedule an inspection or provide emergency after hours service. Request a repair and improve your indoor air quality today.

Please note: This information is provided for advice purposes only. Regulations differ from state to state, so please consult your local authorities or an industry professional before proceeding with any work. See our Terms & Conditions here.

Published: 2021-04-29

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I called them in the morning, and they were at my doorstep within a few hours. The technician was quick to identify the problem, had the necessary parts, and repaired my AC unit in no time.

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My AC was acting up, and I was worried about a hefty repair bill. However, the technicians quickly identified a minor issue, fixed it, and didn't overcharge me. I appreciate their honesty and expertise in troubleshooting the problem.

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Thorough filter cleaning left no room for concerns, resulting in cleaner air and AC that requires less maintenance. Our home's air quality has improved dramatically, and we couldn't be happier with the outcome.

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