Why Is My Car AC Making A Whistling Noise (& How to fix it?)

There’s nothing better than an ice-cold air conditioner keeping you cool during the peak of the summer months.

But that enjoyment can end abruptly, the moment you hear a whistling or squealing noise coming from the car.

1) Loud Squealing

When it comes to a car’s air-conditioner, there are two possible sounds that can be generated. The most common of these is a loud squealing noise that appears to come from the engine compartment itself.

There are a number of potential causes of this squealing noise, but in most cases, it is the result of worn-out bearings or belts.

Belts & Pulleys

Car belt and pulley

One of the most common noises created when an air conditioner is turned on is the sound of the belts screeching and squealing.

While older cars used a V-belt, most newer cars operate with a serpentine belt.

Regardless of the type of belt that a car uses, it must stay in good contact with the pulleys at all times.

As belts age, they tend to stretch out and become loose.

Newer vehicles with a serpentine belt, have a tensioner that is designed to automatically tighten the belt as it ages.

However, older vehicles do not have a tensioner and must be adjusted from time to time.

When the belt becomes loose, it begins to slide through the pullies, rather than stick to them.


Car engine bearings

But there are a lot of components within an engine compartment that can also squeal and screech whenever the air-conditioner is turned on.

The automatic tensioner on serpentine belt engines has a bearing in it.

These bearings can wear down over time.

And when too much pressure is applied to them they will make noise.

However, the sound of a worn-out bearing is deeper than the sound of a slipping belt.

2) High-Pitched Whistling

For the most part, squealing noises will come from the engine compartment.

But, whistling noises may also develop within the air conditioning system that can only be heard while inside the car.

If you hear a whistling noise the moment you turn on the air-conditioner, then it’s possible you have a leak in the vents themselves.

Misaligned Duct

If you have been in an accident recently, or have even taken your car in for an oil change, it is possible that one of the ducts under the dashboard may have come loose.

The vents are generally not bolted at each section, rather each section is inserted into the next.

If one of those vents becomes misaligned, then it can create a whistling noise as the air passes over the gap.

Cracked HVAC Case

Likewise, the HVAC case itself must be opened by a technician whenever they check the filter.

If you have recently had an oil change, then the technician may have also checked your air filter.

If the case is not reassembled properly, it can cause an air leak that will whistle whenever the air-conditioner is turned on.

At the same time, if the case was cracked or damaged during the inspection of the air filter, this can also create a whistling noise.

Foreign Items in Duct

Although not as common in newer vehicles, older vehicles can produce a whistling noise in the event that a foreign object becomes lodged within the duct.

This could be something as simple as a piece of paper or other item being inserted into or falling down the ducts when the air-conditioner is not being used.

Sometimes, these items can be pushed up against the side of the vent, resulting in a whistling noise.

Diagnosing the Problem

It’s important to first diagnose whether the sound is coming from inside the car or outside the car.

Once you are able to determine the source of the sound, fixing it can be a lot easier.

Inside the Car

Inside the car

Naturally, the first place you will be at when the air-conditioner is turned on is inside the car.

Once you turn on the air-conditioner and you hear the whistling noise, lean your head around to see if you can pinpoint the source of the sound.

If it’s a high-pitched whistling noise, you should be able to determine if it is coming from under the driver-side dashboard, or the passenger side.

If you cannot pinpoint the location of the sound simply by listening inside the car, then you need to get out while the air-conditioner is still running.

Outside the Car

Once you are outside the car, carefully close the door making sure not to lock your keys inside.

If the sound goes away the moment you close the door, then the sound is coming from inside the car and not from the engine compartment.

However, if you still hear the noise then it’s time to investigate the engine compartment itself.

check car engine

If the sound is actually coming from the engine compartment, then shut off the air-conditioner and turn off the car before opening the hood and checking the belts for any wear and tear.


Fixing the Problem

After you are able to pinpoint the source of the noise, you can then focus on fixing the problem.

If the whistling noise was coming from inside the vehicle, then start by simply checking the air filter box to see if it is loose or cracked.

If it is neither, then you might need a technician to pull apart the dashboard in order to realign the ducting.

However, if the noise is coming from the engine compartment, then you need to inspect the belts.

Check the edges of the belt for any fraying.

Both V-belts and serpentine belts will begin to fray at the edges after they become loose.

If it is a frayed V-belt, then you can simply replace it.

However, if it is a frayed serpentine belt, you may need special tools to change the belt.

Lastly, if the belt is not frayed and you notice black marks on the inside of one of the pulleys, then there is a possibility that you have a bad bearing.

Bad bearings generally have a deeper tone to them because they are grinding metal against metal.

If it is a bad bearing, then you will need to take the car to a mechanic to have the pulley and bearing replaced.

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