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Why Is My Air Conditioner Making a Whistling Noise?

Do you hear a grating, high-pitched whistle coming from your vents? If so, it’s probably driving you crazy.

Here’s why you’re hearing that sound: Your A/C system has low return airflow, which means it isn’t getting enough air through its return vents.

Many problems can cause low return airflow, but here are 4 of the most common:

  • Dirty air filters

  • Blocked return vents

  • Closed dampers

  • Too many closed doors

We’ll go over these problems in more detail and discuss what you can do to fix them. But first, let’s look at how low airflow causes your air conditioning system to produce that whistling sound:

Why low airflow causes whistling

An A/C blower pulling in air from the home.

Your air conditioner's blower constantly circulates air in your home. But if your blower isn’t receiving enough air to circulate because something’s blocking or restricting airflow (like the problems we discuss in the next section), then it’s essentially “starved for air.”

If your system is “starved for air,” it means there’s more pressure and velocity, which means you’ll hear a louder and higher sound.

Think of it like whistling compared to normal breathing: When you whistle, you have to pucker and tighten your lips to create a small passageway for the air to pass through, which makes the high-pitched sound. But when you’re breathing normally, your mouth is wide and open and the air you exhale silently.

While that whistling sound can be annoying, the good thing is that it’s alerting you of a problem in your system. Low airflow can damage your system and raise your energy bills, so you’ll want to fix whatever’s causing the problem ASAP.

Now let’s go into the specifics of each airflow problem...

4 airflow problems you can solve right away

Dirty filters

If your filter looks like the one on the right, it’s dirty and you should change it.

Similar to using a strainer while cooking, your air filters pick out unwanted contaminants from your home’s air. But when the filters get too dirty, they restrict airflow and can cause overheating problems.

Solution: Change your air filters every 3 months at a minimum, and preferably every month during the summer.

Blocked return or supply vents

A return vent in a stairwell.

Your return vents are large vents that are usually located in a hallway, staircase or open area. If something is blocking them, like furniture or heavy dust or debris, then your system isn’t getting enough air.

A supply vent.

Your supply vents are the grates with levers that actually provide air to your home. If these are closed or blocked by furniture, you’re system is going to have low airflow.

Solution: Clean the return vent grill and remove any furniture that may be blocking airflow. Make sure your supply vents are all open (even in rooms you don’t use).

Closed dampers

Dampers are metal valves in your ductwork that you can shut to prevent air from being delivered to certain parts of your home.

Solution: Locate the damper levers near your inside unit and make sure they’re aligned with the ductwork to allow airflow.

Too many closed doors

If too many doors are closed in your home, then the supply air has to sneak under the small gaps under the door to the return vents (usually located in a hallway or stairway). This makes your blower work even harder to pull in more air, which causes the whistling noise.

Solution: When possible, keep your doors open to allow proper airflow.

Try all of these DIY repairs, but if those aren’t solving the problem, it’s time to call a professional...

When you need to contact an A/C professional

The airflow problems we just covered can be solved by any homeowner. However, sometimes that whistling sound is caused by bigger problems that only a certified expert can properly fix.

These include airflow problems like…

  • A return grille that’s too small, which means the same amount of air is traveling through a smaller area. That increase of pressure could be what’s causing the whistling sound.

  • A lack of return inlets, which means a professional may have to install one so that your system can receive proper airflow.

  • A malfunctioning blower. Sometimes there’s an issue with the blower itself, either with the wheel or fan that carries a whistling sound into your home.

  • Leaky ducts. If your ductwork has cracks or openings, air passing through them may cause a whistling sound. Leaky ducts also waste money and energy, so you should contact an expert to repair them.

  • An oversized system. This is the most expensive problem to replace because it means that your air conditioning system is moving too much air for your ductwork to handle. Again, large amounts of airflow in a tiny space leads to more pressure and velocity, which could be causing that whistling sound.

Need a professional to get rid of that whistling sound?

Contact Cool Today for an air conditioning repair estimate. We’ll send one of our trusted technicians to your home to diagnose the problem and give you an honest repair quote.

We’ve been serving Southwest Florida since 1963.

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