Why Does My Air Conditioner Smell?

8 Common AC Odors and What to Do About Them

When your air conditioner kicks on, you expect cool, clean air, not a nasty surprise for your nose. If you’ve noticed a strange odor coming from your AC, you’re not alone. Many homeowners in Cherry Hill, NJ, experience this issue, especially during the peak of summer or right when the system is turned on after months of downtime.

The good news? Most air conditioner smells have specific causes and reliable solutions. And when in doubt, you can always count on Jersey Boys Plumbing, Heating, and Air to clear the air and keep your home comfortable.

Why Does My AC Smell Bad?

Your air conditioner works by circulating air through filters, coils, ductwork, and drain lines. Over time, moisture, dust, bacteria, or even pests can build up in these areas, causing unpleasant smells to develop.

Some smells are harmless. Others could signal a more serious issue, like mold growth, electrical problems, or even a gas leak. That’s why it’s important to understand what each smell could mean—and how to respond.

The 8 Most Common Air Conditioner Smells (And What They Mean)

1. Musty or Mildew Smell

Smells like: Damp towels or a wet basement
Likely cause: Mold or mildew inside your AC, especially on the evaporator coil or in the ductwork

What’s Happening:

Moisture in the system—often from a clogged drain line or humid air—can lead to mold growth. This is particularly common in humid summers like those in Cherry Hill.

What You Can Do:

• Change your air filter (it could be trapping moisture and mold)
• Make sure your drain line isn’t clogged
• Schedule professional cleaning with Jersey Boys to sanitize the system and eliminate mold at the source

Pro Tip:

Consider installing a UV light in your system to kill mold spores and keep the air clean.

2. Dirty Sock Smell (a.k.a. Dirty Sock Syndrome)

Smells like: Gym socks or stinky feet
Likely cause: Bacteria growing on the evaporator coils

What’s Happening:

The cold, damp coils inside your AC can become a breeding ground for bacteria. When the system runs, it blows those smells straight into your home.

What You Can Do:

• Replace your filter regularly
• Schedule a deep coil cleaning
• Consider UV light installation to prevent future growth

3. Burning or Electrical Smell

Smells like: Hot plastic, smoke, or gunpowder
Likely cause: Electrical issues like a motor overheating, a wire short, or a damaged capacitor

What’s Happening:

If you smell burning, your AC system may have an overheating part or a failing component. In some cases, it’s just dust burning off after a long winter. But if the smell is strong or persists, shut the system down immediately.

What You Can Do:

• Turn off your AC at the thermostat and breaker
• Do not turn it back on
• Call Jersey Boys Plumbing, Heating, and Air for fast, professional repair

Important: A persistent burning smell could pose a fire hazard; don’t ignore it.

4. Rotten Egg or Sulfur Smell

Smells like: Rotten eggs, sulfur, or decay
Likely cause: A gas leak or dead animal in the ductwork

What’s Happening:

Natural gas is odorless, but utility companies add mercaptan—a chemical that smells like rotten eggs—to help detect leaks. It’s also possible that an animal (like a rodent) got trapped in the system and passed away.

What You Can Do:

• If you suspect a gas leak, leave the house immediately and call the gas company or 911
• If the gas company rules it out, contact Jersey Boys to inspect and clean your ductwork

5. Skunk Smell

Smells like: A skunk sprayed near your vents
Likely cause: Gas leak near your HVAC intake

What’s Happening:

Mercaptan, the same chemical that gives gas its smell, can resemble the odor of a skunk. Your AC might be pulling this scent in from a nearby leak.

What You Can Do:

• Turn off your system and evacuate the home
• Contact your gas provider for an emergency inspection

6. Chemical or Exhaust Fume Smell

Smells like: Sweet chemicals, exhaust, or nail polish remover
Likely cause: Refrigerant leak or oil leak inside the AC

What’s Happening:

When refrigerant leaks, it often releases a sweet or chemical smell. This not only affects your indoor air quality but can also damage your AC and increase energy bills.

What You Can Do:

• Shut off your system immediately
• Call Jersey Boys for refrigerant leak detection and repair

7. Cigarette Smoke Smell

Smells like: Stale cigarette smoke
Likely cause: Smoke particles trapped in your filter, coils, or ducts

What’s Happening:

If anyone has smoked indoors, your HVAC system may have absorbed the odor into its internal components. Every time your system runs, it can release that smell, causing it to smell like cigarette smoke inside.

What You Can Do:

• Replace your filter
• Schedule a duct and coil cleaning
• Avoid smoking near return vents or indoors

8. Sewage or Methane Smell

Smells like: Raw sewage or methane gas
Likely cause: A nearby backed-up sewer line is leaking near your HVAC intake

What’s Happening:

If your AC smells like sewage, the issue may not be with the HVAC itself. A broken or backed-up sewer pipe can release methane into the air, which then gets sucked into your AC system.

What You Can Do:

• Contact a licensed plumber immediately
• Schedule an HVAC inspection to check for entry points

What To Do When Your AC Smells Bad

1. Change your air filter – It’s the easiest first step
2. Check for moisture or puddles – Mold loves water
3. Turn off your system if you smell burning or gas
4. Call Jersey Boys Plumbing, Heating, and Air – We’ll diagnose and fix the issue fast

How To Prevent Air Conditioner Odors

• Replace air filters every 1–3 months
• Schedule annual tune-ups with Jersey Boys
• Keep drain lines and coils clean
• Install a UV light to kill mold and bacteria
• Don’t smoke indoors or near vents
• Keep your outdoor unit clear of debris

Preventative maintenance is the best way to avoid unpleasant surprises, and it keeps your system running efficiently, too.

Need Help in Cherry Hill, NJ? Call Jersey Boys Plumbing, Heating, and Air

Whether your air conditioner smells musty, burnt, or just plain bad, our team is here to help. At Jersey Boys Plumbing, Heating, and Air, we offer expert AC inspections, cleaning, maintenance, and repairs across Cherry Hill and the surrounding areas.

• ✅ Licensed & insured
• ✅ Fast scheduling
• ✅ Honest service
• ✅ Local experts who care

📞 Contact us now or book your AC service online—we’ll help you breathe easier in no time.

Frequently Asked Questions (FAQ)

Why does my AC smell musty when I turn it on?

It’s likely mold or mildew that built up during downtime. If the smell goes away quickly, it’s probably harmless. If it lingers, schedule a cleaning.

Is dirty sock syndrome dangerous?

Not usually, but it indicates bacteria and mold in your system. It can worsen allergy symptoms and should be professionally cleaned.

Can I fix a smelly AC myself?

You can start by replacing the filter and checking for standing water. But deeper issues—like moldy coils or refrigerant leaks—need professional attention.

Why does my AC smell like chemicals or exhaust?

It could be a refrigerant leak or an overheating motor. Both can affect your health and your AC’s performance. Turn off the system and call for service.