• Ben Loy

Does your air conditioner smell musty?

Updated: Jul 4, 2021

Air Conditioner smells - 9 great cleaning tips

Air conditioners can sometimes smell bad. From my experience, it is mostly odor coming out from the air conditioning vents.

The smell can be accompanied by a "short of breath" feeling and headaches. This can really mess up your day.

One possible reason is mold on your ac vents. Here is an example:

Keep reading and learn how to get rid of that stink from your AC.

Here is the deal:

Your air conditioner smells. What can you do about it?

A smelly air conditioner can blow several different smells and odors.

Here is the not complete list of smells people report. If you are reading this, I am sure you can relate to one of them.

AC smells like: gas, burnt plastic, electrical burning smell, vinegar, sweet, dirty socks, moisture, rotten eggs, mildew, sour, chemicals, urine, feet, fishy smell, OR just bad, musty, stinks, generally smelly, and so on.

The smell can be bad and can make you give up on turning on the AC, making your day worse.

No all is lost though. There is plenty you can do.

In this article, I share my way of getting rid of that smell. A set of tips I follow to reduce and sometimes eliminate those bad smells. My own AC odor treatment.

Tips for preventing the air conditioner smells

Here is the list of tips. They can work individually but I recommend trying at least a few combined for better results.

Run the air conditioner on Dry Mode

The Dry Mode is shown on the remote by a symbol that looks like a drop or a bunch of drops.

This mode dries the air.

It may reduce the smells for a while. You can toggle between Cool Mode and Dry mode.

Enable X-Fan mode

X-fan mode, when enabled will cause the air conditioner to keep running, without the outer unit running (i.e. the condenser will turn off), for a few more minutes.

The purpose of that is to make sure the evaporator unit (the inner A/C part) is dry before the air conditioner completely shuts down.

This should prevent mold and bacteria buildup since those need water to prosper.

Create a drain line siphon

Bad smell can get through the air conditioner drain line back to the indoor unit,

Especially if your drain line is connected to your home sewer line.

What I did was creating a siphon in the pipe using a T connector. This is the same principle as the toilet siphon which prevents bad smells from entering the bathroom.

You can use a standard universal T-piece adapter(paid link). Make sure the adapter fits the diameter of the drain hose.

Run the A/C on Fan Mode

In Fan mode, the inner unit runs continuously while the compressor is not running at all.

Meaning, no cooling or heating, only air at room temperature.

When the A/C is not cooling, it doesn't create moisture on the coils. This creates the right environment for A/C drying.

Run the A/C for 3-5 hours on Fan mode. You may notice that the smell is gradually disappearing.

The air conditioner consumes less electricity running of Fan mode since the compressor is not working.

Try this tip every 2-4 weeks and reduce that bad smell.

Dry water pooling in the indoor unit

If accessible. look for water pooling at the bottom of the inner unit, drying it with a cloth can reduce bad smells.

Water pools can promote bacteria and mold.

Water pooling can occur when the drain line is clogged. Make sure water drip normally out of the drain line when the AC is cooling.

Use a coil cleaner spray

Coil cleaners usually spray foam that clings to the coils and cleans them from dust and mold. The coil cleaner spray may also kill bacteria.

They do not always come as foam, but this is usually the case.

It is recommended to clean the inner unit's coils with a designated coil evaporator cleaner(paid link).

How to use: Remove the filters, make sure the air conditioner is OFF. Spray the foam, wait for few minutes and run the air conditioner again.

TIP: Usage instructions may change from product to product. Always follow the manufacturer's instructions when using air conditioner cleaning products. Wear protective gear.

Here is an example of a cleaner.

Clean the air conditioner filters

Clean them every month or so. If you can't at least every 6 months and at the beginning of the hot season.

You can usually clean filters with water. If you choose that, make sure you put them back when they are completely DRY.

If your filters are old and broken, buy new ones.

I use a vacuum cleaner to clean my filters. Much faster and less messy.

Use a UV light air purifier and sanitizer

I have to admit that I have never used this product myself.

I thought it can be a nice addition to this list though. For your consideration.

Like potable drinking water systems that utilize UV light to eliminate bacteria, this solution offers the same principle for maintaining bacteria and mold-free evaporator coils.


  1. This device needs an electrical outlet. Make sure you have one close to your unit.

  2. Open your unit and locate a potential place to put the UV light.

  3. Make sure it fits the inner part of your evaporator. Find out what are the sizes.

  4. Read the installations instructions. Make sure you can do it yourself.

Clean the evaporator fins

Evaporator fins may collect dust over time. That dust prevents optimal airflow through the fins which causes moisture to condense on the fins.

Moisture and dust create mud and that will clog the entire system and may lead to a bad smell.

One simple solution: maintain clean fins.

One way is cleaning the fins using an evaporator fins brush(paid link).

Use it to gently clean the fins and remove dirt, ideal before using the spray cleaner I mentioned above.

What causes that smell from your air conditioner?

Let's talk about the cause and the result.

The cause: Moisture.

When running your AC, the coils condense the humidity in the air since the coils are cooler. That creates water pools that are drained via the drain line.

That is normal so far.

If, for some reason, that moisture can not find its way out of the air conditioner indoor unit, by drainage or by evaporation, the moisture pools in the AC unit and on the coil. Typically, also in the air vents.

The result: Mold, bacteria, and nasty smell.

The environment created, especially the moisture and darkness is a breeding ground for bacteria and mold.

Those build up on the coils, air vents, drain line, etc.

In return, that mold and bacteria create a bad smell that we all try to get rid of.

There are few more reasons for a bad smell from AC. For example, burning smell from AC.

In this case, when you believe or sense that there is an electrical issue or potential fire issue, do not delay and contact an electrician or AC professional.

To conclude

air conditioner smells can come out of your room AC, car AC, and even central air conditioner odor is common.

Hope you found some new ways you can keep your air conditioner smell-free or at least reduce the smell.

Let me know if you tried some of these tips and how well did it work for you.

If you have a doubt when DIYing your air conditioner, I recommend you contact a professional.


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