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Why Is My Car AC Making Noise?

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

AC system noises can help you diagnose system issues.

AC system noises can help you diagnose system issues.

Is your car AC making noise? Often, paying attention to the type of noise coming from your air conditioning system can lead you to the specific component or that part of the system at fault:

  • Worn clutch
  • Bad compressor
  • Faulty hoses
  • Loose component mounts

The following section headings describe specific noises you may hear coming from your car AC system. They'll tell you what they mean, so that you can concentrate on the specific part of the system with the potential problem.

So head over to the relevant section and check whether there's actually a real problem going on with your AC system.

Making your diagnosis and repair easier:

To identify and, if necessary, check components, have the repair manual for your particular vehicle make and model on hand. If you don't have this manual yet, you can buy an inexpensive, aftermarket manual from Amazon. Haynes manuals come with step-by-step procedures for many maintenance, troubleshooting and part replacement projects you can do at home. So you'll recoup your initial investment soon.

Index

1. My AC Makes a Clicking or Squealing Noise

Video: Checking a Noisy Blower Motor

2. I Can Hear a Vibration Type of Sound

3. My AC Makes a Rattling, Groaning, or Knocking Noise

4. My AC Makes a Buzzing Sound

5. My AC Makes a Whistling or Hissing Noise

6. AC System Noises as a Diagnostic Tool to Save Money

A worn AC compressor clutch may produce a loud clicking noise.

A worn AC compressor clutch may produce a loud clicking noise.

1. My AC Makes a Clicking or Squealing Noise

A low, clicking sound coming from the AC system is normal. Probably what you hear is the AC compressor clutch engaging. However, a worn clutch can produce a loud click. So you can take this as a warning sign.

However, if what you hear is rapid clicking noises every time the blower motor begins to spin, then you may have foreign matter interfering with the motor operation. The next video shows you how to check the blower motor and a possible fix to your problem.

Often, when the clutch is at the end of its service life, loud clicks may turn into a squealing or rattle noise as the clutch connects.

But there can be other reasons for a squealing AC system:

  • A clutch contaminated with oil.
  • A seized compressor.
  • A faulty pulley or pulley bearing.

The AC compressor in your vehicle uses the engine's serpentine belt to operate. If you haven't found the source for the squealing sound in the AC system, check the drive belt.

If the serpentine belt in your vehicle is a few years old, or has been in service for 100,000 miles (160,934.4 km) or more, you may want to replace it. Some vehicles, specially older models, use more than one drive belt to run other accessories. If necessary, check those belts as well and consult your vehicle repair manual.

Checking a Noisy Blower Motor

Check that AC system hoses aren't touching other components.

Check that AC system hoses aren't touching other components.

2. I Can Hear a Vibration Type of Sound

Vibration sounds coming from the AC system may appear to happen inside the cabin of the vehicle. Usually, what you hear is an AC hose causing a vibration as it rubs against another hose or part in the engine compartment.

Pop the hood open and take a look at AC system hoses. See if they are in contact with another hose or component. Look for scratches or rubbing spots.

If necessary, reroute hoses using nylon cable ties.

Check that AC-compressor mounting bolts are tight.

Check that AC-compressor mounting bolts are tight.

3. My AC Makes a Rattling, Groaning, or Knocking Noise

Often, rattling, groaning, or knocking noises come from an AC compressor or other system component with loose or damaged mounts. The sound may come and go at times.

  • Check the compressor mounts. Tighten the mounting bolts or replace the mounts, as necessary.
  • Rattling or knocking sounds may also originate inside the compressor. The noise may increase as you accelerate. This means a faulty component is producing the noise and the compressor needs to be checked. In most cases, the compressor is replaced with a new or rebuilt unit.
  • Also, check drive belt(s) for wear or damage and replace it, if necessary.

Other common sources of AC rattling noises:

  • Compressor pulley bearings
  • Blower motor
  • Compressor clutch
Overfilling your car's AC system with refrigerant may cause a buzzing sound.

Overfilling your car's AC system with refrigerant may cause a buzzing sound.

4. My AC Makes a Buzzing Sound

Often, an AC buzzing sound may appear short after the system has been serviced and topped off with refrigerant. You may hear a buzzing sound when turning on the AC system. This isn't normal.

Usually, a buzzing sound indicates the system has been overcharged with refrigerant. This may lead to performance issues (poor cooling) and, worse, damage to system components. If left unattended, you may end up replacing the compressor.

Visit the shop that serviced your car's AC system, tell them about the sound, and have them check the system.

High and low pressure areas equalize after AC system is turned off, producing a hissing noise.

High and low pressure areas equalize after AC system is turned off, producing a hissing noise.

5. My AC Makes a Whistling or Hissing Noise

Most of the time, a whistling or hissing noise coming from the AC system is not a sign of a system problem.

After you turn off the AC, you may hear a hissing sound as high pressure and low pressure areas equalize in the system. As refrigerant flows through a metering component, it makes a whistling or hissing sound.

Service the AC system as recommended by your car manufacturer.

Service the AC system as recommended by your car manufacturer.

6. AC System Noises as a Diagnostic Tool to Save Money

No vehicle AC system is completely noise-free. But unusual noises are often the first sign of trouble. Don't ignore them.

Soft or loud noises may signal a potential and serious problem in the making. Taking care of these noises can save you time and money.

AC system noises are not the only ones that may come from under the hood, though. Belts, suspension components, the steering system, pulleys and some other engine components and systems can become noisy and may signal trouble as well.

This guide helps you identify common AC noises, and where in the system they may be coming from. Once you know there's something worn with your car AC, you can take it to the shop or, better yet, try to make the necessary repairs yourself with the help of your vehicle repair manual.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 Dan Ferrell