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Why Does My Air Conditioner Smell Like Mildew?

The smell of mildew coming from your air conditioner can be both unpleasant and toxic. Identifying the culprit of the foul odor will allow you to tackle the problem head-on.

Your air conditioner smells like mildew because moisture has accumulated and allowed mildew to grow inside the unit. Air conditioner drip pans, coils, ductwork, and air vents are areas of an air conditioner that are prone to moisture accumulation and odor-causing mildew growth.

Identifying the source of the stench from within your air conditioner and properly treating the mildew with a cleaning application is something I will discuss. Also, understanding how to get rid of mildew odors and maintain a clean appliance free of toxins will be covered. Handy tips are listed to ensure you have a gameplan ready to fight the stink.

Places Mildew Grows on Your Air Conditioner:

  • Drip pans –  Air conditioners are equipped with drip pan trays that can clog, and moisture causing mildew to form. Make sure your drip pan is drained properly and doesn’t allow water to become stagnant.
  • Internal coils – Inside air conditioners are coils that can be exposed to moisture from within and cause mildew. These coils are often found within the air conditioner; however, they can be cleaned.
  • Filters – A simple check of your appliance’s filter can uncover moisture build-up and require a filter change. Filter size and types are different depending on your make and model appliance.
  • Air Vents – Vents can be overly exposed to moisture, causing fungus and mold to grow as a result. These areas often need to be scrubbed with a brush to remove mildew. 

Do-It-Yourself Tool-Kit To Eliminate Odor:

  • Bucket 
  • Screw Driver
  • Plastic Spray Bottle
  • Bleach or Cleaning Agent
  • A toothbrush or Small Brush
  • Rubber Gloves

Types of Cleaning Products Used To Fight Stink:

  • White Vinegar: This ingredient is mildly acidic, can kill up to 82% of mold species.  DO NOT dilute the vinegar. This must be applied with a sponge or by directly spraying onto the mildew.
  • Hydrogen Peroxide: Use a bottle of 3% peroxide, and apply with a spray bottle or cloth. Not meant to be diluted.
  • Baking Soda: This natural alternative fights odor. Add .25 tbsp(5g) of baking soda to hot water and shake vigorously. Use a spray bottle, and spray on to apply.
  • Bleach: Mix one cup of bleach with 1 gallon of hot water and use accordingly. This everyday household product kills germs on contact, according to the EPA(Environmental Protection Agency).
  • Lysol Disinfectant: The active properties within the household Lysol multi-purpose cleaner’s ingredients contain agents that are said to fight and eliminate mildew. This product is ideal for removing mildew and easy to apply by simply just spraying on.
Lysol Multi Purpose Cleaner Power White & Shine with Bleach, 32 Ounce

A Where To Begin Guide:

  • Unplug your air conditioner- When rolling up your sleeves to combat odor in your air conditioner, be sure to unplug your appliance before you begin cleaning work.
  • Choose your cleaning solution- After gathering your tool-kit, decide on a cleaning product or homemade cleaning solution that you think is fit for the task of cleaning. RMR-141 Disinfectant Spray Cleaner is top-rated by the EPA and should be a go-to choice in buying a competent mildew remover.
RMR-141 Disinfectant Spray Cleaner, Kills 99% of Household Bacteria and Viruses, Fungicide Kills Mold & Mildew, EPA Registered, 32-Ounce Bottle
  • Follow the application instructions- Depending on what your cleaning solution calls for, follow the instructions on applying the product. Make sure you wear protective gloves when handling cleaning products.
  • Use a brush to apply when necessary – Some cleaning solutions will require that you need to apply the product with a toothbrush or small brush to get into the crevices of the air conditioner, to the root source of the mildew. Do so thoroughly with an unger 2-in-1 brush, perfect for mildew tasks, as it works with ease.
Unger 2-in-1 Bath and Tile Brush
  •  Identify ALL areas of possible mildew growth – In some cases, depending on the age and condition of your air conditioner, you may have multiple areas of your unit that needs cleaning. Choose a cleaning strategy that best fits your task(s).

The Do and Don’ts of Deep Cleaning:

When undertaking a project to remove the musty smell of mildew from your air conditioner, it is important to thoroughly clean your appliance to the extent that it is completely free of fungus growth. Below is a checklist of do’s and don’ts to keep in mind if you self-clean your air conditioner.


  • Identify ALL of the areas of mold within your appliance.
  • Use different cleaning methods depending on mildew’s location.
  • Use a screwdriver if needed to unhouse the internal parts within.
  • Vigorously scrub away at mildew growth to remove entirely.
  • Clean all areas near and around the mildew growth.


  • Don’t only just spray on a cleaning solution without working to remove the actual mildew build-up.
  • Disassemble or remove specific parts from within your air conditioner to clean.
  • Continue to leave small trouble spot areas untreated throughout your appliance.
  • Use cleaning agents without protective equipment as directed (gloves, brush, other cleaning tools).
  • Work to clean your air conditioner while it’s plugged into a power source.

When To Call the Pros:

  • Time & Budget – Maybe a do-it-yourself approach is not your best option, and because of budget, you can call in the pros to do the dirty work. Plus, maybe you think your time is too precious.
  • When it’s a new unit, some newer air conditioners may be covered by limited time warrantees and cover a cleaning option with coverage.
  • If you have a weak stomach – The harsh lasting smell of mildew can be stomach-turning for some. Forego cleaning the unit yourself and opt to call in a pro if you hate the idea of having to withstand tuff odors.
  • Everything feels overwhelming – For some, the complicated idea of having to follow a bunch of steps and apply genuine elbow grease to remedy an appliance-related issue is just too much to ask. This is a case in which you should call a pro.

Opting To Replace Your Air Conditioner

Factors to consider when deciding to replace your unit:

  1. The age and condition of your air conditioner do not warrant any further repair.
  1. Access the degree of repair necessary to decide that the unit is worth spending the time or money to rehab.
  1. The cost of a new air conditioner versus the prospect of keeping a mildew infested appliance that still works? Desiccant air conditioning.
  1. Understand any additional costs of seeking professional services, in addition to the cost of a potential replacement. Don’t overspend to fix your problem.

Final Thoughts

The challenge with mildew stink is locating the source of the mildew on your air conditioner, which forms as a result of moisture build-up, and produces odor. Many remedies exist to fight the mildew stench coming from those areas of your air conditioning unit, and repair costs vary depending on if you choose to do the repair project yourself or consult professionals to assist you.

In worst-case scenarios, some may find investing in a new unit is worth it compared to investing the time, effort, and money to fix your existing air conditioner. Having a clear understanding of what it takes to undertake this nature project will help you decide on a remedy that best suits you. Being mindful of the total cost and time for the project will be key in helping you find the best solution. The CDC reminds people, mold can be treated.


  • Nicole Sutton

    Nicole Sutton is an enthusiastic writer and knowledgeable contributor to She offers a plethora of knowledge to the platform, with a background in environmental science and a profound curiosity with all things connected to temperature regulation. Nicole's interesting and informative writings assist readers in making informed decisions about home heating, cooling, and climate control.

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