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Why Does My Home Air Conditioner Smell Bad, and What to Do About It

There’s nothing more annoying than a home air conditioner that smells bad on a hot day when you just want to cool down. But you may be able to figure out what your problem is based on the type of smell that you’re getting.

The most likely scenario is that your AC unit isn’t properly ventilated or that you have dirty coils. But there are other smells and potential issues that are worth exploring, too.

We’ve put together this article to explain them. Keep reading to find the most common home air conditioner smells and instructions for what to do about them.

Types of home air conditioner smells

Before diving into these, try to pay attention to when the smell comes up. Is it just after you turn your AC on? Or maybe it’s strongest near a certain vent? These pieces of information may be able to help you figure out what’s behind your problem.

  1. Fire smell

If you have a fire smell coming from your home air conditioner, that usually means something is burning within your AC unit. There are tons of different electrical parts and wires in your system, which are often coated in plastic. If you have overheating issues with your unit, this excessive heat may melt the plastic coatings.

It’s also possible that you just have excess dust in your system. This can sometimes burn off and lead to a fire-like smell.

What to do about it

First, try to see if you have excess dust in your system. If you do, it will burn off on its own, and the smell will go away naturally.

But if you clean your air conditioner regularly, it’s likelier to be a burning component. And in that situation, you would want to turn off the system immediately and call a professional for help.

  1. Skunk or gas smell

AC manufacturers have to add a chemical called mercaptan to imbue natural gas with a rotten egg odor. That way, when it leaks, it’s very easy for homeowners to know.

This is a serious problem that you need to deal with right away. Skunk, gas, and sulfur smells coming from your HVAC system are all signs of a gas leak.

What to do about it

If you smell something like a rotten egg from your air conditioner, take the following steps, in order:

  1. Switch off your gas line
  2. Open up as many windows as you can
  3. Get out of your home
  4. Call your gas company to come to take a look

Remember, natural gas is toxic to humans. So you really need to take this seriously for the sake of your family.

  1. Rotten egg smell

If you don’t smell gas or sulfur but do smell something like a rotten egg, it could be caused by a dead animal that’s stuck in your vents somewhere. Things like birds, rodents, and insects can all cause these problems when they get stuck in your ductwork.

What to do about it

The only solution to this problem is to get the dead animal out of your ductwork. That starts by locating the specific vent where the smell is strongest.

You can then use a screwdriver to take off the plate and look for the animal. If you find it, remove the animal and clean the spot where you found it.

However, that animal may also be out of sight. In that situation, you may just want to call an HVAC technician out to fix the problem for you, as it will be tough to do on your own.

To prevent this problem from happening in the future, you should look into pest-proofing your system a little better. You can do that by sealing off any entry points into your ductwork.

  1. Musty smell

A musty, dirty-sock-like smell is one of the most common foul scents that people get when they complain about a home air conditioner that smells bad.

This is usually caused by water accumulation, either in your drain line or drainage system. When that happens, mildew and mold can grow, which causes the smell.

But your system may also be emitting this smell because of a dirty air filter. Air filters in humid climates can sometimes retain moisture and grow mildew and mold themselves.

What to do about it

Fixing this problem may be as easy as performing some routine maintenance, such as cleaning your system and changing your air filter. You may want to call a professional out to clean your refrigerant lines and ducts as well.

Here is a more detailed article on the subject: How to remove the musty smell from your air conditioner

In the future, you can avoid this problem by being better about performing routine maintenance on your air conditioner.

  1. Vinegar smell

A vinegar smell coming from your air conditioner is often the result of an electric motor problem. These can sometimes emit ozone when they malfunction.

It’s also possible that you’ve got a dirty filter, some mold somewhere in your ductwork, or even condensation in your coils and a clogged drain pan.

What to do about it

The first thing to look at for this smell is your filter. If it’s dirty, change it and see if that fixes your problem.

You may also need to give your air conditioner a thorough cleaning to remove any lingering sources of smell.

  1. Cat pee smell

Some people also complain about getting a cat pee smell in their AC unit. This is often an indication of mold.

The cat pee smell won’t come from the mold itself. But the mold creates mycotoxins, which can be dangerous for your family to breathe in.

What to do about it

Mold is a serious problem that can be hazardous to your health. So if you think that you’ve got this in your AC unit, you’re going to need to call over a professional to have them take a look and solve the problem.

  1. Cigarette smell

This smell is pretty straightforward. If you smoke in your home, then your air conditioner will eventually start to emit air that smells like smoke as well.

Components like your evaporator coil and filter can hang onto some of this smoke and then redistribute it throughout your home.

What to do about it

The best solution to this problem is to quit smoking in your house. Otherwise, the smell is going to keep coming back because the system will keep taking in more smoke, even after you clean it.

But if you have decided to quit smoking in your home, then you can fix the issue by cleaning your evaporator coil thoroughly and changing your air filter.

  1. Sewage smell

Finally, your home air conditioner may sometimes emit a sewage-like smell. This is often the result of a dry P-trap. These tend to allow gases from the sewers to come back up into your home.

It’s also possible that you’ve got a ruptured sewer vent pipe somewhere. Or maybe you have a backed-up sewage line. These could all be reasons why you’re smelling sewage in your home.

What to do about it

There are a few different steps you can take to fix this problem, and the right solution will depend on the source of the smell.

For example, every month, you should turn on all of your sinks so that they fill up the P-trap. When you do this, it creates a kind of seal that protects against sewage gas coming into your home.

If you do that already and it isn’t working, then it’s likelier to be one of the other problems we touched on above. At that point, it’s best to call a professional.

Sewage gases can be toxic to breathe, so be sure to tackle this problem as soon as you notice it.

  1. Sweet ether-like smell

If you’re smelling this, you likely have a refrigerant leak, and your AC unit uses R22 refrigerant. Refrigerant is a chemical substance that your AC unit uses to cool down warm air. If it leaks, it can bring down the performance of your system quite a bit.

You may notice a slightly sweet smell as well if you have this problem. It resembles the smell of freshly mowed grass. Refrigerant is toxic and can be hazardous to the environment, so it’s important to be careful when dealing with this issue.

How to tell if you have a refrigerant leak

Smell is just one factor that you can look at to determine whether you have a refrigerant leak. Here are some other signs you can use to corroborate your suspicions:

  • Unusually high energy bills
  • A bubbling or hissing sound coming from your AC when it’s on
  • Ice forming on your refrigerant lines or evaporator coils
  • Difficulty in keeping your house as cool as you want it to be

If you’re experiencing one or more of these issues alongside the chemical smell, there’s an even higher chance that you have a refrigerant leak.

What to do about it

If you have a refrigerant leak, it’s best to contact an HVAC repair person. They’ll handle the problem safely so that you don’t risk exposing your family or the environment to the harsh chemical.

This issue can cost between $230 and $1,600 to fix. But your costs will depend on the severity of the problem and where you’re located, among other factors.

Michael Joseph