Reasons Why Your AC Smells and Fixes

If your AC smells bad, there could be a few issues, depending on the type of odour coming from your unit. For example, if your AC smells musty, it could be due to mould or mildew growth. If your AC smells like rotten eggs, it could be due to a natural gas leak. And if your AC smells like burning plastic, it could be due to an electrical issue.

Learn more about what different smells can mean when they come from your AC and how you can alleviate the issue ASAP. Maintenance can help you avoid AC issues, including smells! 

Here are some main issues of why your AC smells bad. 

1) Clogged Water Drain 

When your AC condensation basin gets clogged with debris, it can cause the unit to smell. If you have a water softener, or if you live in a humid climate, this is especially likely to occur.

To fix this, you’ll need to clean the basin using a water hose, and then use an AC drain cleaner to remove any built-up debris. If you can’t get to the drain itself, you can put the cleaner directly into the unit to dissolve the gunk.

2) Exhaust Leaking

If your AC’s exhaust is leaking into your home, it could be creating a foul smell. Your AC’s exhaust is supposed to go out a vent that’s separate from the air vents in your home. It’s rare that you’ll smell exhaust in your home, but it can happen if the vent has come loose or if there are holes in the exhaust pipe.

To fix this, you’ll need to check the vent to ensure it’s properly installed and has no holes, and then use a flexible duct to seal off the leak.

3) Gas Leaking

If your AC smells like rotten eggs, it could be due to a natural gas leak. If this happens, you’ll need to contact the gas company immediately to get the leak fixed before it becomes an issue. Depending on the location of the leak, you may be able to get it fixed right away, or it could take a few days.

In particular, methyl mercaptan could be getting into your ductwork and causing the smell in your home. The gas is invisible and has no colour, but it’s incredibly pungent.

4) Dead Animals

If you’re noticing a bad smell near your AC, it could be due to a dead animal. Critters like squirrels, raccoons, and skunks can get into your ductwork, and it’s not a smell you’ll forget!

In order to get rid of this smell, you’ll need to get your AC ductwork cleaned. Once you’ve had the ductwork cleaned, you can seal up any holes you find in the system.

5) Mildew and Mold

If your AC smells musty, it could be due to mould or mildew growth. This is a more common issue in areas with high humidity, and you’ll notice the smell once the air conditioning kicks on.

Mildew and mould are the most common culprits, but your AC could also be contaminated with other types of fungus. 


The bottom line is that when your AC smells bad, it’s usually due to an issue with the unit, not the air quality in your home. The best way to deal with this issue is to have your AC ductwork and equipment professionally cleaned.

Legacy Heating can help you identify the sources for your air conditioning unit to smell bad. We provide air conditioning repair so that you’ll have a sweet-smelling space in no time at all.

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