Why Does Your AC Smell? 7 Odors Explained and Solved (2024)

A strange smell coming from your air conditioner can turn a hot summer day into a nightmare. Whether it’s a musty odor or something more alarming like a burning smell, identifying the cause early can save you from costly repairs and health risks. In this guide, we’ll explore the 7 most common AC smells, what they mean, and how to fix them.

1. Musty or Moldy Smell

Causes

A musty or moldy smell is one of the most frequently reported odors from AC systems. Excess humidity or moisture can lead to mold and mildew growth within the HVAC system, especially in the drain pipe, drip lines, or ductwork. This smell might also occur due to dirty air filters, particularly if your AC has been inactive for a while in a humid climate.

Solutions

To address this, have a professional clean the AC lines and ducts and improve the drainage system. Replacing air filters regularly and scheduling annual or bi-annual AC tune-ups can prevent this issue. Installing a whole-home dehumidifier can also help by removing excess moisture from the air, which not only prevents mold but also allows you to set your thermostat to a higher temperature, saving energy and money.

2. Rotten Egg or Sulfur Smell

Causes

A sulfuric or rotten egg smell could indicate dead rodents or other animals in the ductwork, or it might be a sign of a gas leak. Natural gas is odorless, but utility companies add a chemical called mercaptan to give it a distinct smell. A ruptured sewage pipe near your air ducts could also cause this odor.

Solutions

If you suspect a dead animal, a professional can help remove it and inspect for damage. For potential gas leaks, immediately contact your gas company to shut off the supply and avoid using any open flames. If you suspect a ruptured sewage pipe, a licensed plumber should inspect and repair the issue.

3. Dirty Socks or Stinky Feet Smell

Causes

This unpleasant smell often results from dirty air filters, clogged condensate drain pans, or stagnant water within the system.

Solutions

To eliminate this odor, replace air filters regularly and have a professional clean the evaporator coils and unclog drain pans. Adding a bit of distilled white vinegar to the drain pan can help prevent future growth of algae and fungi.

4. Burning Smell

Causes

A burning smell could mean that a component in your AC system is overheating, such as the motor or wiring. Dust settling in the unit after a period of inactivity can also cause a burning odor when the system is first turned on.

Solutions

If you smell burning plastic or another alarming scent, turn off your AC immediately and contact a professional. If it’s just dust burning off, the smell should dissipate quickly. However, if the odor persists, turn off the system and seek professional help.

5. Skunk or Gas Smell

Causes

A skunk-like odor is another sign of a gas leak. As mentioned, the additive mercaptan gives natural gas its distinct smell.

Solutions

If you detect this smell, follow the same steps as for a gas leak: contact your gas company to shut off the supply, and call a professional for repairs.

6. Car Exhaust Smell

Causes

This smell typically indicates a refrigerant leak. Refrigerant absorbs heat from your home, and a leak can not only reduce cooling efficiency but also release harmful chemicals into the air. Older systems using R-22 refrigerant are especially problematic due to the environmental impact of chlorofluorocarbons (CFCs).

Solutions

If you suspect a refrigerant leak, contact your local HVAC company to repair the leak and top off the refrigerant. Regular maintenance, including checking refrigerant levels, is essential for optimal system performance.

7. Cigarette Smoke Smell

Causes

If smoking has occurred inside the home, tobacco particles can accumulate in the AC filters and evaporator coil. When the system is turned on, these particles are recirculated through your vents.

Solutions

The best solution is to smoke outdoors to prevent this issue. Regularly changing air filters and scheduling AC tune-ups can help remove lingering odors. There are also other options to improve indoor air quality such as air scrubbers, house plants, and air purifiers!

Final Thoughts

No matter what strange odor is coming from your AC system, it’s always a good idea to call a professional to diagnose and fix the problem. Preventative maintenance, including regular air filter changes, annual tune-ups, and the installation of indoor air quality products, will keep your HVAC system running smoothly and odor-free.

If you live in the Delaware Valley/Greater Philadelphia area and would like to find comfort within your home, visit our websiteor give us a call at 215 - 245 - 3200 to learn more.

This entry was posted in Comfort Tips, Air Purifiers, Air Filters, Air Conditioning, Aerus Air Scrubber