Why Does My AC Smell? (Solutions for Musty, Fishy Odors)

While air conditioning units are definitely one of the most sought-after home appliances when temperatures start heating up, there are also quite a few things that can go wrong.

One of the most common is foul odors coming from the unit. If yours is starting to smell funky, then keep on reading because we’re here to figure out why and help you solve it!

Common Types & Causes of Bad AC Smells?

Plants and Fresh Air
Smells Burnt

With so many different electrical components, if you smell something burning, it’s most likely that one or more of them are burning. In this case, turn the AC off right away and call up an HVAC technician who can fix it. However, if it’s been a while since you’ve turned it on and it starts smelling burnt, it’s more likely that the dust that’s gathered on the unit is burning off. This won’t last long, so if you’re still dealing with it after a few days, you need a pro to help.

Smells like Gas/Car Exhaust

This is almost always due to a leak in your refrigerant line, which can also be hazardous to the environment and those who inhabit it. The smell is due to the fluid being heated/burnt and needs immediate professional revision. Keep things well-ventilated in the meantime by keeping windows open.

Smells like Rotten Eggs

If your AC smells like rotten eggs, it’s possible that a dead rodent/birds/other animal has become stuck in the unit. As time passes, this foul odor will begin to make an appearance. Try to first turn off the air conditioner and take a screwdriver to remove the cover and remove the unfortunate creature. If you don’t feel comfortable doing this, you can also have a professional inspect it.

Smells like Mildew/Musty

This is probably the most common smell of the bunch and is often due to water accumulating in the drain pan or drip lines. This can, over time, cause mildew to form and therefore a musty smell can increase. If you live in a humid environment, then this could also just be because you have dirty filters where moisture has built up. In either situation, you want to contact a professional to get the lines cleaned.

Smells like Fish

This is also often caused by a dead animal stuck inside the unit. If not this, it could also be due to a burning electrical component such as a wire, electrical shielding, a plastic part, etcetera. If none of these are the case, then it’s also possible that mold has begun to grow inside the unit. No matter which one of these applies to your situation, you’ll need an HVAC technician to come and clean/repair it.

Smells like Vinegar

This can happen for a variety of reasons. One is that there’s excess condensation on the coils, your filter isn’t working correctly, your condensate pan is clogged, or there’s mold in the ductwork (if yours isn’t a ductless model).

Smells like Pee

An AC might smell like pee because of mold inside the unit. The pee smell doesn’t come from the actual mold, but from the mycotoxin byproducts it creates. Mycotoxins make ammonium which gives it the pee smell.

Smells like Smoke

A smoke smell in your AC is mostly caused by dust and dirt buildup in the air vents, filters, coils or housing. It could also be from an overheated motor or fan. Excess heat can burn the wiring insulation.

How to Get Rid of Bad Smells Coming From Your AC

Generally speaking, you’re going to take the same steps to get rid of bad smells coming from your unit.

  1. Turn off the power
    Before you do any kind of maintenance on an electrical unit, you must turn off the power to keep yourself and others safe. You’ll find the specific power shut-off and make sure you’re 100% sure you’ve done this before proceeding.
  2. Change the air filters
    Just as a general rule of thumb, you’ll want to replace your filters every 2 months. However, if you have pets or you have someone in your home with allergies, this may need to go down to every 30 days.
  3. Clean evaporator coils
    After you’ve already switched out your filters, you can proceed with cleaning the evaporator coils. You should do this ideally with a foaming coil cleaner that can clean them effectively yet won’t damage anything. This in itself will often solve your odor issue.
  4. Clean condensate lines
    Look for the drain line near the outside unit that drips water as the unit is running. If this water is anything but clear, make sure to flush the condensate line with a solution of bleach and water.
changing an AC filter

People Also Ask (FAQ)

Is a smelly air conditioner dangerous?

It definitely can be, as the smell itself could be from an unhealthy mold or animal carcass. In every case, it’s better to get it looked at or clean it out yourself.

Can dirty air conditioner filters make you sick?

Yes, they can! Dirty air conditioner filters can mean dirty air, and we should never be breathing in polluted air. Always aim to stay as safe as possible in the home!

Does a dirty AC filter affect cooling performance?

Yes, it does! Dirty AC filters make cooling and overall operation less efficient. Even the top-performing AC brands are only good when they are clean!

How do I know if my AC filter is dirty?

One of the most popular ways of doing this is by hanging up a clean white sheet a few inches away from one of the AC vents for at least an hour. If the sheet turns gray/brown, then your filter is dirty.

Can air conditioner filters be washed?

Reusable filters can be washed and replaced. Can you put a wet filter in your air conditioner? No, never. You want to make sure it air dries completely before putting it back in, as it can create ice and other problems. Also, make sure you’re never washing and replacing disposable filters.

Should I hose down my air conditioner?

This answer may be surprising for many, but yes, you absolutely can! If it’s really hot out and your unit isn’t able to take it, you can spray it down with a garden hose to cool it. Doing so will even help clean the unit and make the condenser run more efficiently.

What is a Dirty Sock Syndrome?

This happens when you switch from using your heater to the AC. As dust gets trapped in the filters and your evaporator coil of the AC gets hooked up, the dust and mildew/mold can create a foul smell. It’s not usually dangerous but can definitely provoke wheezing and coughing.


We hope that if you’re experiencing a foul odor coming from your AC unit, that our guide is able to nip it in the bud. If you follow these simple steps, then we’re sure that you’ll be able to live in a cool, clean, and pleasant environment from here on out!

Josh Mitchell

Josh Mitchell

My name is Josh and I am obsessed with DIY and improving my family home. HVAC topics can be tricky for homeowners so I decided to share my knowledge on the subject. When I am not working on DIY projects, you can find me at the beach or my local coffee shop.