7 Reasons Why an Air Conditioner Smells & How to Eradicate Them

Imagine this: You arrive home after a long, sweltering day, tired and sweaty.

Eager to find relief from the heat, you kick off your boots, jump on the sofa, and switch on your trusty air conditioner. But instead of being greeted by refreshing cool air, an unpleasant odor permeates the room, forcing you to turn off the AC hastily.

As frustration sets in, you wonder why your air conditioner is doing this, and of course, there’s the concern that this unwelcome odor might lead to even more expenses down the line.

Let’s explore common odors from air conditioners that you might encounter, the potential health risks associated with them, the underlying causes, and practical solutions to eliminate these.

Types of Air Conditioner Smells, Possible Causes, and What You Can Do

One of the most significant challenges for homeowners is addressing unpleasant odors from their air conditioning units. However, it can be difficult to determine why an air conditioner smells, decipher the type of smell indicating a specific issue, or even recognize the scent of Freon, which is also known as refrigerant.

Here are the details of every smell you can experience if you own an air conditioner, along with ways to resolve it. So, let’s take a look:

1. Air Conditioner Smells Like a Car’s Exhaust?

An air conditioner does not run on an internal combustion engine. So, there is no reason why your air conditioner should smell like running car exhaust. However, your air conditioner does make use of some fluids, and when heated, they can smell like exhaust fumes.

A smell from an AC such as this most likely means there is a leak in your refrigerant line. A refrigerant is a cooling agent inside your air conditioner, and a leak can impact its performance. Moreover, it releases chemicals into the air, deteriorating the quality of indoor air and thus being hazardous to the environment and your health.

A Freon leak would smell like sweet chloroform or, in simpler terms, just like your car’s coolant but with a sweetish odor.  So, even though it is an almost odorless gas, you can still detect the smell. But Freon, being heavier than air, does not linger around in the air for long and drops down to floor level pretty quickly.

If your AC emits a chemical-like smell, you should get it checked promptly by a professional. A Freon leak can be dangerous, and a certified HVAC specialist will repair it in no time.

In the meantime, crack open the windows and make sure your home is ventilated. This will keep the smell out and prevent any hazardous effects from the chemical leak.

2. Air Conditioner Smells Like Cigarette Smoke?

If you smoke at home, then there is a chance that your AC will eventually end up smelling like stale cigarette smoke. This unpleasant smell can cause allergic reactions and headaches.

Your evaporator coil and filter absorb the odor from cigarette smoke. When you turn on the air conditioner, the embedded tobacco particles are knocked loose and sent back into your home through the AC’s vents, creating an unpleasant atmosphere.

Clean your filters in a timely manner. If you often forget to check your filters, smart thermostats for mini-splits can help by providing timely notifications when it’s time for a cleaning. Also, do not forget to clean your AC regularly.

3. AC Smells Like Something Is on Fire?

There are a lot of electrical components within your air conditioning unit—circuit boards, power wires, fans, compressors, etc.

If your AC smells like burning gunpowder or plastic, it probably means one or multiple of these components are burning. In this case, immediately turn your air conditioner off and consult your local professional for a solution.

Do not attempt to do a DIY with this sort of problem; it can be dangerous.

Another common reason for such an air conditioner smell is that dust can settle within your unit after long inactivity. This dust can burn off and emanate a bad smell when turned on after a long time. This is only temporary and is nothing to be too concerned about.

However, if the smell remains, the AC starts to malfunction, or the smell is highly pungent, you must turn off your unit and call your local HVAC expert immediately.

Related: Signs Your AC Tune-Up is Due: Keep your AC in Top-Notch Condition

4. Are You Smelling Rotten Eggs From Your AC?

A foul or rotten air conditioner smell is usually the result of dead rodents or critters stuck in the AC. This is a characteristic and distinct smell that you surely cannot mistake for anything else.

Insects and birds can nest in your air conditioner and can, unfortunately, get trapped in the equipment. With time, these dying animals emit unpleasant smells. As soon as you turn your air conditioner on, it can discharge a foul smell into your home. Dying or stuck animals can also damage different components within your AC.

It’s best to always pest-proof your unit to avoid such a nasty scenario and having your AC smell like a carcass. But, of course, you can always call a technician to help remove the dead animal or fix this issue yourself!

You will need to locate the exact duct from where the stench erupts, use a screwdriver to remove the cover, and then carefully remove the carcass.

It can be tricky if the dead animal is not in sight. Keep a torch within quick reach. Once removed, gently wipe the area clean and ensure it is dry. It is recommended that you check your ductwork to ensure nothing is damaged and seal any entry points.

Related: Rodent Proof Ductwork: 6 Ways to Get Rid of Rats in Your Air Ducts

5. Is Your Air Conditioner Smelling Like Dirty Feet or Socks?

If your air conditioner smells like dirty socks or feet, mold or bacteria growth within the system is likely the culprit. This unpleasant odor, often referred to as “dirty sock syndrome,” occurs when moisture accumulates on the evaporator coils and isn’t properly drained away.

The dark, damp environment inside the AC unit provides an ideal breeding ground for mildew and bacteria, which can produce a musty, foul smell. This issue is more common in environments with high humidity and typically arises when the air conditioner switches between heating and cooling modes.

To eliminate the odor, the first step is to clean the evaporator coils, which can be done either by a professional or as a DIY project if you are familiar with AC maintenance. Cleaning the coils removes mold and bacteria buildup, helping to get rid of the smell. Additionally, ensuring that your unit’s drain lines are clear and functioning properly is crucial to prevent future moisture accumulation.

6. Do You Smell Gas and Feel Like There’s a Skunk in the House?

This air conditioner smell is the most alarming one on this list. More often than not, this indicates gas leakage within the system, specifically Methyl Mercaptan.

Natural gas has no smell on its own, but utilities and gas distributors add Methyl Mercaptan to give it a distinctive odor. This ensures immediate detection to prevent any serious harm from gas leakage.  

If your AC smells like skunk spray, you won’t be mistaken. This means that gas is leaking into your ductwork.

Immediately turn off your gas supply at the first sign of such a smell. As a second step, contact your utility, who will detect the source and repair the problem.

7. Getting a Moldy or Musty AC Smell?

The most common foul smell experienced by ACs is stale and dingy. If your AC smells musty, the general cause is a clogged drain line due to water accumulation in the drain pan or drip lines (or ducts in the case of ducted systems). This can cause fungus or mold to grow.

If your indoor ductless unit leaks, you might even see visible signs, such as water dripping down your wall.

Another reason for such a smell can be dirty filters. For example, if you live in a hot and humid climate and turn your AC on after a long period of time, moisture can accumulate in your filters. A rule of thumb is to clean your air filters every two weeks and replace them in three-four months.

Here’s a detailed AC filter guide that will help you keep them in top shape.

You will need to contact a professional and get your AC’s lines and ducts thoroughly cleaned. This will only remove the unpleasant smell. In case of a leakage, the source will also need to be fixed to prevent further problems.

Related: Why is Your Indoor AC Unit Leaking Water?– 8 Common Causes & How You Can Fix Them

Take Precautions Before Doing a DIY

Now that you might know why an air conditioner smells, it is time for action. But before attempting any DIY projects, it is crucial to take necessary precautions to ensure your safety and the proper functioning of the equipment involved. Here are a few essential guidelines to keep in mind:

• Seek Professional Help for AC Repairs: If you have the expertise and required tools, you can repair your AC yourself. However, if you lack technical knowledge or are ill-equipped, it is recommended that you avoid attempting AC repairs on your own. Contacting a professional technician is the safest and most reliable option.
• Familiarize Yourself with Manuals: If you feel confident in handling a DIY project, thoroughly review your air conditioner’s maintenance and operating manuals. Understand the equipment’s specifications, guidelines, and safety instructions provided by the manufacturer.
• Personal Protective Equipment (PPE): Whenever engaging in a DIY project, it is essential to prioritize personal safety. Wear appropriate personal protective equipment, such as gloves, safety goggles, and clothing suitable for the task.
• Gather the Right Tools: Before starting any DIY project, ensure you have the necessary tools and equipment required for the job. Using the appropriate tools increases efficiency and reduces the likelihood of accidents or damage to the equipment.
• Turn Off the Power: Before working on your air conditioner, turn off the main power supply to the unit.

Delaying necessary repairs will only worsen the condition of your AC, potentially leading to the need for a full replacement. It’s always better to address issues early by getting your AC checked in time.

Related: AC Replacement Guide – Is It Time for an Upgrade?

Health Issues Associated With Smelly Air Conditioners

To effectively tackle this problem, acquiring knowledge about the various odor-related issues associated with air conditioners becomes crucial.

• Respiratory Issues:

Inhaling air contaminated with mold, mildew, or bacteria from a smelly air conditioner can lead to respiratory problems, including coughing, wheezing, and shortness of breath, especially for individuals with asthma or allergies.

• Allergic Reactions:

The presence of mold spores and bacteria can trigger allergic reactions, resulting in symptoms like sneezing, runny nose, itchy eyes, and skin rashes.

• Infections:

Prolonged exposure to mold and bacteria can increase the risk of developing infections, particularly in individuals with weakened immune systems. This can include sinus infections and bronchitis.

• Headaches and Fatigue:

Poor indoor air quality due to a smelly air conditioner can lead to headaches, dizziness, and overall fatigue as your body struggles to cope with the contaminated air.

• Aggravation of Chronic Conditions:

For people with pre-existing health conditions such as asthma, chronic obstructive pulmonary disease (COPD), or other lung diseases, exposure to mold and bacteria from a smelly AC unit can exacerbate their symptoms, leading to more frequent and severe flare-ups.

Related: Can Air Conditioning Make You Sick? Here’s the Truth

Why an air conditioner smells bad? Hopefully, now you have the answer to the question!

All the factors above make for an unpleasant experience, whether it’s ducted or ductless air conditioning. So, the next time you come home and experience an unpleasant odor, you know exactly what it could be and what you need to do to fix the problem.