Why does my AC smell?

Does your AC smell like musty or like mildew? Learn the common causes—like bacteria, mold, or clogged drain lines—and how to fix it.

Strange Odors Coming from Your AC?
Here’s What Might Be Causing Them

You’re not alone. This is a common issue, especially in older homes or when AC maintenance has been overlooked. We are here to give you information and tips to help you find a solution to your problem. We know that for families with allergies, autoimmune conditions, small children, or newborns on the way, air quality is critical.

What Causes That Bad Smell in Your AC?

Have you ever turned on your air conditioner and noticed a strange, unpleasant smell—almost like dog urine?

If your AC smells like dog urine when it runs, the most likely culprit is bacteria or mold buildup inside the system. Moisture collects on the evaporator coils, creating the perfect breeding ground for bacteria. Over time, this can produce a strong, musty, or urine-like odor.

Here are some specific reasons why this might be happening:

How long has it been since you changed your air filter?  A clogged filter traps dust, pet hair, and dander, which can lead to bacteria growth.

Have you check your AC condensate drain line?   If your AC’s condensate drain line is blocked, standing water in the drain pan can encourage mold and bacteria to thrive.

Do you have water leaking inside of your unit?   Water leaks inside the unit can create the same conditions as a clogged drain pan, leading to bad smells.

Pet Access to the Outdoor Unit – If your dog has access to the outdoor AC unit, they might actually be urinating on it. This can cause lingering odors that get pulled into your system.

How to Get Rid of the Smell:

First start by replacing the air filter – A new filter helps improve air quality and reduces bacteria buildup.

Next, check the drain pan – Make sure the drain pan isn’t overflowing, and clear any blockages in the condensate drain line.

Make sure to clean the outdoor unit – If you suspect pet urine, rinse the unit with a hose and mild disinfectant.

Finally, ventilate your home – Open windows and use fans to help circulate fresh air while tackling the problem.

If the smell persists after trying these steps, it’s best to have an HVAC technician take a closer look. A professional can:

Clean the evaporator coils – These coils can be difficult to access and require special cleaning solutions.

Inspect for leaks – If condensation is leaking inside the system, it could be creating hidden mold issues.

Check for mold growth – A technician can identify and eliminate deeper bacterial or mold problems.

At Blue Dot Air Conditioning & Heating, we understand how important clean, fresh air is for your family’s health. If your AC smells off and DIY fixes aren’t cutting it, give us a call. We’ll help you get your home smelling fresh and clean again!

Contact us today for an free AC inspection!

Frequently Asked Questions

When comparing air conditioning systems, think about the features you care about most. You can look for value, energy efficiency and noise levels and select the model that best matches your needs. ENERGY STAR qualified units, high SEER rated systems and multi-stage systems are all good indicators of air conditioners that will save energy and reduce your energy bills over time.

Yes. Regular maintenance is critical to keep your system running efficiently and ensure you maximize the life of the unit. For a very low cost, you can have peace of mind and enjoy better indoor comfort all year long.

A split system is the most common central air system and includes an indoor unit and an outdoor unit. An air conditioner is an outdoor unit, usually installed in conjunction with a furnace or air handler to provide both heating and cooling comfort.

SEER stands for Seasonal Energy Efficiency Ratio. SEER is the most common way to evaluate an air conditioner’s efficiency and measures how much energy it takes to keep your home at the temperature you choose.