Solving bad air conditioner smells: common causes and solutions

A properly functioning AC unit will release fresh, cool air into your property. Something has gone wrong if your air conditioner smells bad.

We know the last thing you want is for your AC unit to fill your home with foul-smelling air. So, we’ve laid out all you need to know in this expert guide.

Reasons why your air conditioner smells

Malfunctioning AC units can give off a variety of different scents. The type of smell you notice can help you to get to the bottom of the problem.

Common AC odours include:

• Old socks/feet
• Burning
• Musty
• Damp/mould
• Rotten eggs

There are many reasons why an air conditioner can smell unpleasant. Let’s take a closer look at the common causes and try to determine which one is making your AC smell bad.

Leaking gas

Air conditioner units use refrigerant gas to create cool air. You will only smell this gas if there is a leak somewhere in the system. Old air con systems often use Freon refrigerant, which produces a strong sulphur smell.

Not only does this leaking gas smell like rotten eggs, it can be dangerous. Don’t put your health at risk, switch off your AC and arrange a professional repair as soon as possible.

Modern AC units do not use Freon and use a refrigerant gas with barely any odour instead. That being said, you should never ignore a refrigerant leak, even if your house doesn’t smell like rotten eggs!

Dirty components

Dirty parts can cause countless problems for your air conditioner, including a nasty odour. Clogged filters and a buildup of grime on the coils can often result in a burning or mouldy smell.

It is no surprise that air passing through a dirty filter has an unpleasant odour. If your home smells like old socks, your AC unit could be the culprit.

Dead animal in vents

Rodents and small birds occasionally get stuck inside AC systems. If an animal dies inside the vents, you will notice a foul rotten egg smell.

Mould on evaporator coils

Evaporator coils work by removing heat from the air circulating around the AC system. Mould can build up on these parts over time, resulting in a horrible damp smell.

Blocked drain pan

A blocked drain pan can also cause an AC unit to smell like mould. The drain pan collects moisture created during the air cooling process. A blocked or full drain pan is the perfect breeding ground for mould.

Overheating

Dirty AC parts can overheat and circulate a burning smell around your home. Melting components inside the unit also cause a similar type of odour.

Never ignore a burning smell coming from your AC unit. If the system overheats, a bad smell will be the least of your problems!

Infrequent Use

Dirty parts may also be to blame if your air conditioner smells bad when turned on after a long period of inactivity. If infrequent use is the problem, the bad burning smell will go away after a few minutes.

How to fix an air conditioner that smells

Once you have determined the cause of a bad AC smell, it is time to solve the problem. Remember, air conditioner units do not smell when all parts are working correctly.

If your air conditioner smells musty, replace the air filters. You can replace clogged-up filters yourself or hire an AC technician to do it for you.

An air filter replacement is not always needed. If your air conditioner smells like feet or has a musty odour, this can be removed by thoroughly cleaning the filters and other AC components.

A build-up of moisture and mould in the drain pan can also be easily fixed. Remove the excess water and clean the drain pan, taking your time to remove all traces of mould. Once the mouldy water is gone, your AC unit should circulate odourless air again.

When to hire a professional

You may not always be able to fix a smelly AC unit yourself. Professional repair work will be needed if your air conditioner has a refrigerant leak causing a rotten egg smell.

A technician will find the source of the leak, repair the damage and top the refrigerant back up to the required level. An AC specialist can also safely remove dead animals from vents and sanitise the unit.

Do not hesitate to call a professional if your air conditioner smells like burning. An overheating AC is a potential fire hazard and needs to be repaired as soon as possible.

Switch off your AC system the moment you notice a burning smell. This odour may just be dust burning off the different parts, but it could also be a sign of a dangerous electrical fault.

Don’t try to fix electrical faults yourself. This is a job best left to the professionals.

How much do AC repairs cost?

Professional AC repairs have various prices. The type of repair work you need depends on the reason behind the bad smell.

A one-off service can help to eliminate unpleasant smells and costs approximately £70 - £120 per unit. Meanwhile, leak repairs cost approximately £300+ and can stop your AC from smelling like rotten eggs.

Professional cleaning and antibacterial treatments cost £15 - £30. This service will be needed if a dead animal or mould buildup has been causing your air conditioner to smell.

Check out our home air con service cost guide to find out more about professional maintenance and repair costs.

Key takeaways

• AC units can smell for a variety of reasons. Dirty components, refrigerant leaks, mould, electrical faults and dead animals can all cause air conditioners to smell bad
• Cleaning the unit and replacing damaged parts can remove unpleasant odours
• Burning smells should not be ignored. Hire a professional to fix an overheating AC unit – attempting DIY electrical repairs can be dangerous
• Professional air con servicing costs approximately £70 - £120 per unit

FAQ

Why does my air conditioner make my room smell?

There are many reasons why air con can make your room smell. Common causes include clogged air filters, dirty parts, mould buildup and overheating components.

How long does AC smell last?

Most AC smells will stay until the problem is resolved. For instance, you can only get rid of a musty, dirty socks smell by replacing the air filters and cleaning the AC system.

The smell of decomposing animals and mould will get worse over time.

If you haven’t used your AC in a while, the burning dust smell should stop after a few minutes of switching the unit on.

Should I be concerned if my AC smells?

An AC unit should only release fresh-smelling air. You should consider any bad smells as a warning sign.

Switch your unit off and call a professional if your AC has a strong burning smell. Overheating air con systems are dangerous and should be repaired as soon as possible.

How do I get rid of the smell in my air conditioner?

Cleaning and replacing the air filter is the most common fix for a smelly AC unit. Removing mould from the system can also stop unpleasant odours.

If you don’t know what to do, hire a professional. An expert can find the source of the bad smell and fix the problem for you.