AC Smells Musty But Heat Doesn’t

ac smells musty, air conditioner smells

AC Smells Musty But Heat Doesn’t

There’s nothing better than escaping the scorching heat of summer and relaxing in your air-conditioned home. But when you catch a whiff of a strange, musty smell, you need to act fast. What does a musty smell coming from your air conditioner mean?

In short, a musty smell indicates bacterial growth build-up, which forms on the drain, evaporator coil, or in the drip pan or drain line of your AC. Your evaporator coil is in a dark and humid location, so all sorts of mold and mildew can grow, which causes that unpleasant, musty smell. We at Las Vegas AC Repair will cover the steps you need to take to find the source of the musty AC smell and how to fix it, including:

  • Check if your AC drain pan is full
  • Check for frozen evaporator coils
  • See if there is excess moisture in your ducts or vents
  • Identify if there is a blockage in your condensate line
  • Determine if your AC unit is not the right size for your home

Because the air coming from your AC vents isn’t supposed to have a smell, you’ll need an expert HVAC company if you notice the equipment letting off a musty odor a little while after adjusting the thermostat to a cooler setting.

Five Reasons Why Your AC Smells Musty

  1. The Drain Pan is Full
  2. Frozen Evaporator Coils
  3. Excess Moisture In Ducts Or Vents
  4. Blocked Condensate Line
  5. Incorrect AC Size For Home

The first step to getting rid of the smell is actually preventing it from happening in the first place – this is one of the many benefits of having an annual maintenance contract. By cleaning the evaporator coil and treating the drain line, this smelly air conditioner problem can hopefully be prevented.

This is where indoor air quality (IAQ) products come in. These accessories, when installed into a new or existing HVAC system, can kill any existing mold and mildew and keep any new growths from forming. A trained HVAC technician can recommend and install a variety of IAQ products to help keep your heating and cooling system clean and odor-free.

Additionally, ultraviolet lights installed in the evaporator coil will kill any current growth and inhibit any future growth. Ionizers can help also help to kill any microbial contaminants.

Clean A Mini Split Air Conditioner Turn off the power to the unit and unplug it from the wall outlet. Remove the front panel of the unit and inspect for any visible dirt or debris. If you are looking to install a mini split in your garage, there are several things that you will need to consider.

Why Are Strange Smells An Issue?

Whether you notice the smell of dirty socks, rotten eggs, or mildew permeating from your ductwork, all smells indicate an underlying issue with your air conditioning unit.

Sometimes your HVAC unit may emit a burning smell at the start of the cooling or heating season as dust that has settled in your unit burns off. If you smell rotten eggs could mean you have a gas leak or a dead animal in your vents. A dirty sock smell, or musty smell, means you could have a mold issue.

A musty odor typically means there could be contaminants present in your air conditioning system. Because your system is a dark and humid place, it’s a breeding ground for bacterial growth.

A musty smell, not unlike dirty gym socks, began to circulate through the home. “What is it?” I thought. “Where is it coming from?” I change my air filter but to no avail – it’s still there. It is like an air conditioner mildew smell, and now that my nose is more attuned, I can track it down and gasp it seems to be coming from my air ducts! Okay. Great. One part of the mystery is solved. Now that I know where it’s coming from, what can I do about it?

There are all kinds of reasons why your air conditioner smells bad. Some of them are simple fixes, and others are more complicated. We’ll let you know when you can solve the problem yourself, and when you’ll need to call a certified HVAC technician, like Las Vegas AC Repair.

Here is the most common air conditioner smells and how you can solve them. A Central Air Conditioner Smells Like Chemicals If your air conditioner smells bad when turned on, particularly with a chemical odor, isn’t a great sign


If your air conditioner smells like it’s burning, the chances are it probably is. This is one of the worst problems you can have, and we’re tackling it head-on. Your air conditioner is a machine and has a ton of moving parts. Any one of those parts could be faulty from the blower motor to the wiring, or some other mechanical issue.

If the smell continues even after you’ve turned it off, contact the fire department. Use judgment here of course, only do so if you suspect the unit is still actively burning.

Chances are the problem will stop when the air conditioner is turned off. To make sure there’s no power, turn off the disconnect box on the wall near your outdoor condenser.


We’ve covered a major issue, now let’s talk about an easy one. As with the burning smell, if your air conditioner smells like cigarettes, the chances are it is cigarette smoke.

Air Conditioners smells like cigarettes

If you or a loved one frequently smoke in your home, the smoke likely filtered through your ductwork. Those scent particles then embed themselves into your air filter. When you turned on your air conditioner, those particles were knocked loose and sent through your vents and back into your home. To solve this problem, change your air filter. This should be done twice a year at a minimum anyway. Once in the winter and once in the summer.

Ideally, you’ll change your air filters once every 90 days.


Surprise, if your air conditioner smells like something died, it probably did.

The first could be the air handler of your air conditioner. This piece of equipment is what cycles air through the house and runs your air through the air filter. This doubles as your furnace in a traditional air conditioning system, or is in place of it if you have a heat pump, which provides both heating and cooling.

The furnace/air handler is likely located in your garage, a closet, or your attic. All three are favorite places of pesky critters. Depending on the location of your air handler, you would be able to remove the faceplate and get at the critter, but if it’s in your ducting you’ll have to call a professional. If not, an HVAC technician will need to come to locate and remove the problem.


Your air conditioner smelling musty could be by far the worst of the problems listed.

While an air conditioner burning smell might prove to be the most dangerous, it’s usually quickly diagnosed and solved. If mold is present, that means you have a water issue. It could be a leak in your air conditioning system or it could be completely unrelated. When water damager is involved, repairs could get expensive.

If the source of the leak is discovered to be your air conditioner, and it’s still under warranty, replacement of your unit may be covered subject to the conditions of the warranty. Bi-annual system inspections, called tune-ups, keep your air conditioner and furnace working properly and discovers potential problems before they become major issues.


It doesn’t smell like a dead animal, mold, or cigarettes, and nothing is burning. What now?

It just smells like dirty socks or general stink.

Air Conditioner smells like stinky socks, dirty sock syndrome

This air conditioner smell is likely caused by a dirty evaporator coil or clogged condensate drain.

If you have any questions or concerns feel free to contact us today.

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LasVegas AC Repair

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