If your HVAC is working properly, you shouldn’t be smelling anything strange. If you do start to smell something out of the norm, it could be a sign that you might have an HVAC issue on your hands.

Here are a few reasons why an AC smells and what may be causing unpleasant odors.

1. Why Does My AC Smell Musty?

If you’re sitting next to an air vent when the HVAC kicks in and you smell a musty odor, this is most likely caused by excess water that has caused a component of your AC unit to grow mold or mildew. This buildup is typically found on an evaporator coil and inside the air handler. One of the best ways to prevent it is by scheduling regular HVAC maintenance. You can temporarily relieve the issue slightly by replacing your air filters or running an air filter with a box fan to help circulate the air in a specific room.

Humid environments tend to smell mustier since bacteria and mold can build up faster. If you keep noticing a musty smell in your home once your AC has been examined, you may also need to have your air ducts cleaned to remove any mold buildup.

2. AC Smells Like Burning – Help!

Your AC and furnace can both smell like burning, but for different reasons. An AC unit, typically running cool air, shouldn’t smell like burning unless there’s a mechanical or electrical issue. A broken fan belt or a motor that needs to be lubricated can emit odors when they are not working properly. A clogged air filter can also result in an overheated motor. A clogged filter causes your HVAC unit to work harder than it has to and can cause it to burn out faster. Regularly changing out a filter and sticking to recommended MERV ratings based on the capacity of your HVAC unit is a good preventative step.

3. My Air Conditioner Smells Like Vinegar 

You may be wondering why a strange vinegar smell permeates the room when your AC kicks in. There are a few reasons you may start noticing a sour stench.

• Your HVAC’s motor is emitting ozone
• There is too much condensation in your unit
• You have mold and mildew in the ductwork

A clogged air filter might be the main culprit behind this issue as well. When your AC is working overtime to pull in enough air to cycle through the system and it’s blocked by a full filter, it causes the humidity to increase within the unit. Humidity = perfect conditions for mold and mildew growth.

4. Why Do I Smell Rotten Eggs When My AC Turns On?

If you’re smelling rotten eggs when your HVAC system turns on, don’t ignore it! This could be a sign of a decaying critter that got stuck in your HVAC or air ducts, or even more serious, a sign of a gas leak. If you smell rotten eggs when your air conditioning unit is running, leave your home immediately and contact the gas company. If they rule out a gas leak, then you’ll need professionals to inspect your unit and ductwork.

Since strange smells coming from an air conditioning unit can be a nuisance, preventative care like regularly changing an air filter and proper maintenance can go a long way in keeping your system running smoothly. You may have noticed that a clogged air filter can be the culprit behind many of the foul odors we mentioned. Keep your home safe with regular maintenance and enjoy the benefits of good air quality and a healthy home.