Why Does My AC Smell Like Mildew?


If you turn on your air conditioning system only to smell the musty smell associated with mold and mildew growth it can certainly put a damper on your mood. Air conditioning should be refreshing and comfortable, but otherwise undetectable. The only thing more miserable than dealing with the hot, sticky conditions is dealing with a foul smell coming from your air conditioning vents.

If you AC smells like mildew, mold, or other foul odors, it is time to troubleshoot the problem and perhaps call for professional assistance.

Common Causes For Mildew Smell From Your AC

Mold and mildew odors are some of the most common odors found in air conditioning duct work and they can occur for a variety of reasons. A properly functioning air conditioning system should overcome the presence of moisture–the building blocks for mold and mildew growth.
Here are the most common causes for mildew odors to occur in HVAC systems:

  • Dirty or Clogged Filters: If your filter is dirty, clogged, or gets too much exposure to moisture, mildew can begin to grow. Filters trap tiny organic particles that can accelerate mildew growth when exposed to moisture. Check your filters first and if they appear dirty, replace them.
  • Clogged Drip Pan: If your drip pan is clogged, is filling too fast, or has been moved and is no longer positioned where it should be, this can cause mildew growth in and around your air conditioning system. If it is a simple visible clog, you can likely remedy this problem yourself, but more extensive problems may require professional assistance.
  • Clogged Condensate Drain Line: The condensate drain line runs from the coils to the outside of the AC unit and removes condensation created by the coils. If it is clogged, mildew may accumulate on and around your coils.
  • Moist Ductwork: This can occur if your ducts are not well sealed or if your AC system is not removing moisture from the air as well as it should. Excess moisture in your ducts can lead to mold and mildew growth, then spread that odor throughout your house until the source of the moisture is addressed.
  • Internal Problems: Sometimes, the interior parts of your air conditioning system may be dirty or have mildew growth.
    For help with a mildew smell from the air conditioner, contact us and we can help you to resolve the problem.

Frequently Asked Questions

1. Why does my AC smell like mildew?

Mold and mildew odours in your AC can result from dirty filters, clogged drip pans, blocked condensate drain lines, moist ductwork, or internal issues in the system.

2. How can dirty filters cause a mildew smell in my AC?

Dirty filters trap organic particles, promoting mildew growth when exposed to moisture. Regularly replacing filters can prevent this issue.

3. Can a clogged drip pan lead to AC mildew smell?

Yes, a clogged drip pan can cause mildew growth around your AC system. Visibly clogged pans can be cleaned, but extensive issues may need professional attention.

4. What is the role of the condensate drain line in AC odour?

The condensate drain line removes coil condensation. If clogged, it can lead to mildew accumulation on the coils, causing the AC to emit a mildew smell.

5. How does moist ductwork contribute to AC odour?

Poorly sealed ducts or inadequate moisture removal can lead to mold and mildew growth in the ducts, spreading the musty smell throughout your home.

6. Can internal issues in my AC cause mildew smell?

Yes, internal parts that are dirty or have mildew growth can emit a musty smell. Professional assistance may be needed to address these internal problems.

7. How can I get rid of the mildew smell from my AC?

Contact a professional for assistance in identifying and resolving the specific cause of the mildew smell in your AC system.

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