ac in car making noise

Automobile air conditioners usually run quietly, and keep you cool on the hot days. If yours is starting to make strange and unexplained noises, you need to find out why. Before something more serious occurs. 

Here are 6 fairly common A/C noises. With explanations of what may be causing them, and what you can do to fix the problem before it gets any bigger.


Air Conditioner Compressor on 2005 Ram Hemi.



6 Auto Air Conditioning Noises

One of the toughest parts of diagnosing air conditioning noises is making sure they come from the A/C unit. Most strange auto noises tend to sound the same–squeals, rattles, tapping, buzzing, etc.


1) Why is My A/C Hissing When I Turn the Car Off?

The hissing noise you may hear after turning the car off, is almost always a non-issue. When the A/C is running, it creates a high pressure side and a low pressure side in the air conditioner. After turning off the vehicle, the A/C unit will equalize pressure by moving coolant into the low pressure side. This is the hissing sound you hear.

If you hear a hissing sound while the car is running, you need to look into it, or take it to a mechanic to check out. You may have a leak in the unit or one of the hoses that needs attention.


2) Why Does My A/C Sound Like it is Vibrating?

Hearing and/or feeling a vibration type of sound in the passenger cabin can be caused by many vehicle components. One of them you should check out is air conditioner hoses rubbing against another hose or engine part. The noise will sound in the cabin because the A/C vents end there. 

Check all of the air conditioner hoses in the motor compartment to make sure they are not in contact with anything else. If the hoses are close to another component, check them for signs of rubbing or scratching. If they are touching, you will have to devise a system to keep the hoses away from other parts.


3) Why is My A/C Squealing When I Start the Car?

Although many engine parts can cause a squealing noise, the air conditioner is one of the first to inspect when squealing first becomes noticeable.


Serpentine Belt Squeals

The serpentine belt on your vehicle usually runs many engine accessories, including the air conditioner compressor which fills the lines and pumps cool air into the vehicle cabin. The belts usually last for well over 50,000 miles–quite often to 100,000 miles. But they can become worn, cracked, and glazed over time.

It is relatively simple to check your belt (when the vehicle is not running). If you see cracks, excess wear, missing pieces, or the inside of the belt is very shiny, it is probably time to get a new one. If the belt is looking bad, change it. Even if you are not sure it is causing the squealing. A broken belt ends your drive very quickly.

Note: The squeals may not be coming from the A/C unit. The belt could be loose because the tensioner is broken.


Pulley and Bearing Squeals

Rotation of the A/C pulley and bearing can create temperatures up to 1200 degrees F. That amount of heat can dry out bearing grease or boil it out. Dry bearings will squeal. They can also eventually disintegrate because of running without lubrication–causing more damage to pulley, clutch, and A/C shaft. And, of course, more cost. Whether the air conditioning is turned on or not, the pulley, bearing, and shaft are constantly turning at the same speed as the motor. 

Almost all squealing noise coming from your vehicle is due to lack of lubrication. If you hear squealing from the air conditioner or any other part, track it down immediately. And get it fixed. Procrastination will only cost more.

Generally, air conditioner pulleys rarely get damaged. But to replace a worn bearing, you have to remove the pulley and the clutch to get at it. The following video shows you how to remove, and replace, clutch, pulley, and bearing.

Squealing Clutch

Other than the pulley and bearing, your air conditioner’s clutch is probably the most used part of the system. It is constantly clicking on and off according to the demands of the vehicle’s temperature settings. 

The clutch may not engage if the refrigerant is too low. Or it may squeal–sometimes constantly–as it tries and fails to engage. (System sensors will not let the clutch engage if the coolant is too low.)

Clutch parts such as bearings, tensioners, and brackets can wear out. Also, build-ups of moisture, oil, and dirt will eventually cause clutches to wear out.

It is very important to check out any squealing as soon as it begins to save the cost of more expensive repairs.


4) Why Does My A/C Make a Clicking Sound?

Almost all vehicle air conditioners make clicking noises regularly when operating. Some are OK. Some need to be investigated.


Good Clicking Sounds

A low pitched clicking noise is almost invariably the sound of your air conditioners clutch engaging and disengaging as the unit turns on and off. In some vehicles the soft click is followed by what sounds like the motor revving to 2500 RPM. It is only the sound of the A/C compressor kicking into action.


Not so Good Clicking Sounds

A worn clutch will start clicking louder, indicating that a replacement is becoming necessary. When the loud clicks turn to squealing or rattling sounds as the clutch connects, your air conditioner clutch is done and will need to be replaced. 

If you are hearing rapid clicking every time the blower motor starts, it may not be the air conditioner at all. It could be dry leaves, or something else is in the blower grill that is fluttering, tapping, or rustling. This usually happens when something falls down the defroster vents or down the exterior grill at the base of the windshield.


5) Why is My A/C Buzzing When I Just Got it Serviced.

This buzzing is caused by too much coolant having been put into the system. If you hear buzzing, take it back as soon as possible to have the problem fixed. Too much coolant can cause poor performance, and damage other A/C components. If ignored long enough, you could need to replace the entire compressor.


6) Rattling or Knocking Noises

Rattling or knocking noises are often caused by loose or broken mounts. Check and tighten all of the bolts and mounts. If any are broken, make sure you replace them. If mounting bolts becoming loose is a continuous problem, squirt some blue Loctite on them to fix the issue. (Do not use stronger Loctite. You may want to remove the bolts some time.)

More serious knocking or rattling can be coming from inside the compressor. The noise may become louder and more rapid as you increase speed. Have the compressor checked out soon. Unfortunately, it will probably have to be replaced.


Consult an Auto Air Conditioning Professional

Although it is usually fairly easy to diagnose air conditioner noises, fixing them might be a little more complicated. If you do not feel comfortable tackling your auto air conditioner repairs, take it to a shop that specializes in them. This will likely save you time and money in the long run.

A shop usually has almost all the parts in stock. They will be able to recharge the refrigerant when repairs are complete. And should always provide parts and labor warranties for some period of time.

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Author S Krone

A lawyer never retires. So I would just say that I am not as active as I used to be. Now I simply dedicate myself to fishing, my hobby, and my grandchildren. For Business Finance News I write about legal aspects of mortgage policies, mostly regarding the rights of policyholders. I also have articles about personal injuries.

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