Why Does My AC Smell [6 Reasons & Solutions]

A strange odor coming from your air conditioner isn’t just unpleasant.

It’s a sign there may be something wrong with the unit. A healthy and properly functioning AC should not have any smell at all, and if yours does it’s likely time to have it serviced or even replaced.

In this article I will examine why you might have air conditioner odor, looking at six common problems with air conditioners and what you can do about each of them.

Smelly Air Conditioner? Here’s Why

There are six main issues or problems people commonly have with their air conditioners that may be accompanied by a distinct, sometimes quite unpleasant, odor, as well as other symptoms. 

Some of these issues can be dangerous, or present health risks to you and your family, and any of them might cause your AC unit to work less efficiently, making it not as effective in cooling your home and increasing your utility costs – possibly even shortening the life of your air conditioner.

So let’s look at each of these smells in a little more detail.

1. Why Does My Air Conditioner Have a Chemical Smell?

People often report that their AC unit has a bad smell when they turn it on – an odor like chemicals, which is often described as being sweet or reminiscent of paint thinner.

This is a symptom of a refrigerant leak – bad news! – and is also usually accompanied by other symptoms:

• Your air conditioner is not cooling well and not achieving the desired temperature
• Your utility bills are increasing
• You notice a hissing or bubbling sound when the AC is running
• Ice crystals form on the refrigerant lines and/or evaporator coil

Again, not to paint too bleak of a picture, this is not good news, and you will need to have your air conditioner professionally inspected and serviced. If indeed refrigerant is leaking, it can cost hundreds of dollars to have repaired – even over a thousand for central air units and more serious leaks.

If you are dealing with a portable or window-mount air conditioner, especially an older or less expensive one, it might be a very good idea to simply replace the unit, since repairs may be close to the price of a new AC, and a new unit might offer lots of advantages – better cooling, lower energy costs, better reliability and quieter operation among others.

With central air, on the other hand, the main unit may be pretty expensive to replace, and you should at least talk to a qualified air conditioning technician. Even then, though, replacing the central unit might make sense if it is more than about ten years old – older units use freon, or R-22 refrigerant, which is no longer used because of its negative impact on the environment, and so repairs might be even much more expensive.

If you need to replace a full central air conditioning system, it is generally a good idea to work with a local professional, but if you are going to purchase a split air conditioner (with the main unit outside and one or more circulators inside) and are a fairly intrepid DIYer, I very strongly recommend units by Senville, whose smart air conditioners are built beautifully, run quietly and are very powerful and efficient, and are remarkably easy to install. You can check out their whole line at the Senville Product Page.

And if you are replacing a window air conditioner, you might well consider the excellent products from Frigidaire, one of the oldest and most respected companies going, and a real favorite here at Know the Flow for their effectiveness, reliability, and value. You will find a wide selection of excellent window-mount air conditioners on the Frigidaire Product Page.

2. Why Does My Air Conditioner Smell Like Dirty Socks?

Another very common issue with air conditioners is what we call ‘dirty sock syndrome.’ People report that when it is running their AC unit smells musty, like dirty socks, feet, or even a locker room.

Dirty sock syndrome is caused by a dirty evaporator coil. If an AC unit’s filter is not regularly cleaned or replaced, dirt and dust will build up on the evaporator coil, allowing mold and mildew to form.

This is not just unpleasant to smell but can be unhealthy as well.

It is best to have your air conditioner professionally maintained on a regular basis and to keep your filter clean, but if you are already experiencing dirty sock syndrome you will need to have the evaporator coil cleaned. This is a delicate and somewhat difficult job, and the thin fins on the coil are fragile and easily damaged, so while you can do it yourself it might be best to have a qualified professional take care of it.

In extreme cases, the evaporator coil might need to be replaced, and at that point, it might be wise to decide if it is best to do this or – especially if your air conditioner is older – simply purchase a new AC instead.

3. Why Does My Air Conditioner Smell Like Burning Plastic?

A smell like burning plastic coming from your air conditioner – when it is running or even sometimes when it is turned off – is generally a sign of electrical problems, faulty wiring, or a bad or defective component, like the capacitor, the fan motors or belts or the blower.

It is also possible that the electrical problem or faulty wiring is somewhere else in your home, and that your AC unit is circulating the smell throughout the house – especially if you have central air.

Either way, electrical problems are dangerous and can cause fires or additional problems with electrical wiring or other appliances in your home, and should be dealt with immediately.

If you suspect you are having any electrical issues, you should contact a licensed HVAC technician right away to have your unit inspected. If there is any indication whatsoever that the problem might not be with the AC unit, but rather in your home’s wiring, please contact your electric or utility company immediately to report it.

Do not attempt any repairs, or even inspection, of your home’s electrical wiring yourself – always call a professional!

4. Why Does My Air Conditioner Smell Like Gas?

If your AC smells like gas when it’s running, this is usually not an issue with the air conditioner itself, but rather a gas leak somewhere in your house, the smell of which is being circulated by the air conditioner.

This is a very serious and dangerous situation. You should turn your gas off, open up the windows, and leave the house as quickly as possible. Contact your gas or utilities company immediately to alert them.

• Do not smoke, light lighters, matches, or candles in or anywhere near the house.
• Do not return to the house until the utility company clearly says it is safe to do so.
• Do not attempt any repairs, or even inspection, of your home’s gas lines yourself – always call a professional!

5. Why Does My Air Conditioner Smell Like Ammonia?

If your AC unit smells like ammonia or cat pee when running, this is usually a sign of mold in the air conditioner or its ductwork, and what you are smelling are the mycotoxins created by the mold.

Mycotoxins present a serious health hazard, and you and your family should not be exposed to them, so it is best to have your AC unit and ductwork thoroughly cleaned by a licensed professional.

As I mentioned above, it is possible to do this yourself, but the air conditioner coil is fragile and easily damaged – and expensive to replace – so you might end up spending a lot more if there are any problems when you attempt to do it.

Besides that, you need to make sure the ductwork is completely and thoroughly cleaned, as even a small amount of remaining mold can easily multiply and reestablish, so it is a very good idea to have an experienced professional take care of it.

6. Why Does My Air Conditioner Smell Like Vinegar?

Just like an ammonia smell, a vinegar smell coming from your air conditioner might be a sign of mold in the unit or in the ductwork.

A vinegar smell might also indicate that the AC’s condensation is not being effectively removed – the condensate pan or drain line is clogged and backed up.

Often, though, the problem is simply a dirty or blocked AC filter, and so the first step is to clean – or probably best to replace – the filter.

If the problem, and the odor, have not cleared up in a few weeks’ time, you should contact a licensed air conditioner technician to have your AC’s condensation system cleared and cleared, and possibly the evaporator coil as well.

Why Does Your Air Conditioner Smell?

Above you will find the six most common reasons why your air conditioning unit might have a strong, unpleasant smell. 

Any one of these problems can be serious, posing health risks to your family, increasing the risk of equipment failure, and, in some cases, even fire.

All of these issues can also cause your air conditioner to be less effective at cooling and more expensive to run.

Sometimes these issues can be solved by simply cleaning or replacing the AC unit’s filter, but often you will need to get a licensed professional to inspect, clean, and/or service your unit. And again there might be specific dangers or health risks involved, so please look at each specific issue as detailed above for more information.