Window AC Has Bad Smells? Here’s What to Do

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Picture this: You walk into your home on a hot summer day and turn on the window AC. But instead of being met with a cold breeze, you get BLASTED in the face with a terrible stench. EW!

There are many causes of bad smells in an air conditioner. Some are caused by lack of maintenance, others are caused by malfunctioning components.

In this article, I’ll go over a few causes of bad smells coming from a window AC. I’ll also let you know what to do to get rid of bad smells that come from your window AC.

Musty smell in window air conditioner

Do you have a dank, musty smell coming from your window AC? The most likely cause is some sort of growth somewhere:

  • Mold
  • Mildew
  • “Slime” or “Muck”

So what should you do? You’ll need to give your window AC a good cleaning to get rid of the smells.

Here’s what you should do:

  1. Clean the air register
  2. Clean the air filter
  3. Clean the evaporator coil
  4. Clean the drip pan

I’ll go over each of these below.

Clean the air register

The air register is the part of the window AC that the cold air comes out of. Sometimes it’s also called an “air vent”. Mold and mildew can grow in the air vent. In fact, if you see dirty brown or green stuff in your window AC’s air vent, there’s a good chance that the rest of your AC needs cleaning as well.

To clean the window AC’s air vent, follow these steps:

  1. Unplug the window AC from the power outlet. You don’t want to work on the air conditioner while it’s still connected to power—that would be unsafe!

  2. Remove the front panel from the window AC. The front panel is the plastic casing that goes around the entire front of the window AC. In most window AC’s this is one piece of plastic that houses the air register, control panel, and air filter. To remove the front panel, unscrew it from the window AC. In some window AC’s, you will also need to remove the control panel from the front panel.

  3. Use a mild bleach and water solution to clean the front panel and air register. Use approximately 1 part bleach to 3 parts water. The air register will most likely be the dirtiest part, so clean that area thoroughly. Also scrub all of the nooks and crannies on the rest of the panel, particularly the area that houses the air filter.
    After you’re done scrubbing the panel, rinse it off with tap water.

Clean the air filter

The air filter is the part of the window AC that is responsible for filtering out dust, hair, and other particulates from your room’s air. This ensures that the parts inside the window AC don’t get clogged up with particulates from the air inside your room.

Cleaning the air filter is one of the easiest tasks that you can do to ensure that your window AC stays clean and operates efficiently.

To clean the window AC’s air filter, follow these steps:

  1. Unplug the window AC from the power outlet. It is not wise to run a window AC without an air filter. So disconnect the window AC’s power cord before cleaning the air filter to ensure that the AC does not turn on.

  2. Open the air filter access panel. The filter access panel is the large plastic grille on the front of the window AC. Open the access panel to access the air filter.

  3. Remove the air filter from the filter slot. The filter slot in most window ACs consists of small notches that hold the filter in place. Bend one side of the air filter to remove it from the notches, then remove filter from the filter slot.

  4. Clean the air filter. The air filter in most window ACs is a reusable plastic and mesh filter. So you’ll be able to safely rinse out the filter with water to clean it. For normal dust build up, rinse the filter with water and scrub both sides with a soft-tipped nylon brush (such as a toothbrush). If there is sticky grime build up on the filter, use a mild detergent to scrub the filter.

  5. Reinstall the air filter. After cleaning the air filter, allow it to completely dry before reinstalling it into the filter slot. When the filter is completely dry, reinstall it into the filter slot by lining it up with the notches on the sides to hold the filter in place. Keep in mind that there is only one way that the filter can fit in the filter slot, so make sure you put it in the right way. After the filter is reinstalled, close up the filter access panel and plug in the AC.

Clean the evaporator coil

The evaporator coil is the part of the window AC that gets cold. The window AC’s fan sucks air through the cold evaporator coil to cool the air in your room.

If the evaporator coil gets dirty or smelly, then those smells will get into the air in your space.

To clean the evaporator coil, follow these steps:

  1. Unplug the window AC from the power outlet. You’re going to be removing a few pieces of the window AC. So unplug the window AC from its power source so it does not turn on.

  2. Remove the front panel from the window AC. To access the evaporator coil, the front panel needs to be removed from the window AC. There should be a few screws on the sides of the window AC that hold the front panel in place. Remove those screws and take the front panel off to expose the evaporator coil.

  3. Inspect the evaporator coil. If the evaporator coil is a little dusty, then you can get away with just vacuuming the dust out of the coil. But if the coil is caked full of grime and dirt, then you’ll need to do a deeper cleaning.

  4. Clean the evaporator coil. Begin cleaning the evaporator coil by removing excess dust from the coil. Use a vacuum to suck off whatever dust you can from the face of the coil. If there is grime built up inside the coil, spray a coil cleaning solution inside the coil. After spraying, give the coil cleaner 10-20 minutes to break down the grime. Next, use a spray bottle with water to rinse out the coil cleaning solution from the coil. Be sure that all of the coil cleaning solution is rinsed away before proceeding to the next step.

  5. Reassemble the window AC. After you’re done cleaning the evaporator coil, put the window AC back together. Reinstall the front panel and plug the AC back in.
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Clean the drip pan

Have you ever noticed that water comes out of your window AC while it’s running? This water is actually condensation—water that is being “squeezed” out of the air as the AC cools your space.

The drip pan collects this water and gets rid of it by either draining it out or evaporating it.

In older window ACs, water will just drip out of the back of the AC—this is totally normal.

Newer window AC models are self-evaporating. This means that they don’t normally drip out of the back of the AC.

Problems arise when stagnant water collects in the drip pan—mold, mildew, and slime starts to grow. That’s why it’s necessary to keep the drip pan clean. 

It’s also necessary to mount the window AC at a slight angle—that way water can drip out of the back of the drip pan if needed.

To clean the window AC’s drip pan, follow these steps:

  1. Unplug the window AC from the power outlet. You’re going to be taking apart the window AC, so disconnect it from power.

  2. Remove the window AC from the window. Most window ACs require you to remove them from the window to access the drip pan. This can be a cumbersome process, so only remove the window AC from the window if you’re confident in your skills. Every window AC is installed differently, so the tools that are required will be different in every instance. Don’t be afraid to seek out professional help from your local HVAC expert if you are unsure of your abilities.

  3. Remove the front panel from the window AC. In most window ACs, the front panel needs to be removed before taking apart the rest of the unit.

  4. Remove the case from the window AC. The case or “shell” of the window AC is the large metal cover that goes around the top and sides of the AC. You will need to remove numerous screws from the window AC to take off the case.

  5. Clean the drip pan. After the window AC is opened up, you’ll finally be able to clean out the drip pan. Begin cleaning out the drip pan by removing any large debris such as pieces of rust or solid pieces. Next, rinse out the drip pan with water and use a wet/dry vacuum to suck out all the sludge and grime from the drip pan. For stubborn buildup, use a mild soapy water solution and toothbrush to scrub the nooks and crannies in the drip pan. Be sure to clean out the holes in the back of the drip pan to ensure that they are unclogged.

  6. Reassemble the window AC. After you’re done cleaning the drip pan. Follow the above steps in reverse to reassemble the window AC.

Window air conditioner smells like fish

Is there a fishy smell coming from your window AC? A fishy smell coming from a window AC is absolutely not normal. At the very least, it could mean that the AC is dirty and needs to be cleaned. A fishy smell could also indicate a malfunction in the AC unit.

Here are a few reasons why a window AC might smell like fish:

  • Dirty components. If the window AC is dirty, moldy, or grimy, then that could cause a fishy smell. Take a look at the air register, air filter, and evaporator coil to check if any of these components are dirty or smelly. If so, follow the steps above to clean them.

  • Dead animal inside AC. In some rare circumstances, animals such as birds or rodents can crawl up inside your window AC and die. If there is a dead animal in your window AC, then that’s definitely what’s causing the smell. You’ll need to remove the window AC from the window and take it apart to get the dead animal out. Don’t forget to give your AC a thorough cleaning too.

  • Overheated plastic. There are tons of plastic parts inside a window AC. If one of those plastic parts gets extremely hot or burns, it may begin to put out a fishy smell. So what causes the plastic to get hot in the first place? For window ACs, it’s usually due to an electrical component such as an outlet, switch, or wiring inside the AC. I would not recommend trying to troubleshoot an electrical issue without help from an HVAC professional.

Exhaust fume smell from window air conditioner

If you smell an exhaust fume smell coming from your window AC, then it’s most likely due to a refrigerant leak.

If there is an exhaust fume smell coming from your window AC, turn it off immediately. After shutting off the AC, open the windows and doors to ventilate your room.

If there is a refrigerant leak in your window AC, it’s not really worth fixing. Most times it’s cheaper to replace the entire unit rather than pay someone to fix it.

Metal smell coming from window air conditioner

Is there a metallic smell coming from your window air conditioner? Then it’s most likely due to an electrical component failure.

For instance, a burned-out fan motor will give off a metallic smell when the motor overheats. Circuit boards also give off a metal smell when they short out.

If you smell a metallic smell coming from your window air conditioner, then shut off the AC and disconnect its power. The window AC may be able to be fixed, but it will most likely be cheaper to replace the whole thing.

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