How to Quiet a Car AC Compressor: Top 6 Noises & Fixes!

Are you struggling with a noisy car AC compressor? You don’t have to worry about the loud and unpleasant sounds anymore. Check out this in-depth guide on how to quiet a car AC compressor with 5 easy diagnostic measures.

Diagnosing Unusual Sounds From Your Car AC

During the warm season, nothing feels better than driving around as the smooth and cool air from your car’s AC blows your way. However, it can be quite unsettling when you have to deal with rattling, squeaky, and annoying sounds coming from it.

This is normally a sign there’s something wrong with your AC’s compressor. Whilst some problems can be significant, depending on the noises produced, it is generally easy to diagnose the problem and figure out how to quiet a car AC compressor.

Loud Shrieking Sound

This is a common sound reported by many motorists who experience trouble with their car Ac compressor. A loud shrieking sound indicates that there is trouble with the serpentine belt. The serpentine belt is what runs the compressor. Depending on the issue, there are several ways to fix this problem.

  • Spray the belt down with water using a spray bottle and the noise problem should be fixed.
  • If the noise persists, open the hood of your car and check the belt for any wear and tear. If you notice any signs you may need to replace it.
  • If you don’t notice any visible signs, it is a good idea to have the vehicle inspected more thoroughly by a professional.

Buzzing Sound

A buzzing sound is a good indicator that your AC compressor may be damaged. You will notice this sound as soon as you turn on the car AC. The common cause of such a problem is normally excess refrigerant or leaky refrigerant. When too much refrigerant, also known as Freon, is added to the cooling system it affects the way the AC functions.

Too much refrigerant damages the AC compressor as it collects inside it and leads to subcooling below normal temperatures. This, in turn, damages the mechanical parts of the compressor. If you take too long to fix this problem, the damage may be irreversible.

Consequently, you will be forced to replace the entire compressor or cooling system. If you detect this problem sooner, have a mechanic check the compressor to see which parts need to be replaced or cleaned.

In other cases, the problem may be due to a leaking refrigerant. To fix this problem;

  • Check the cooling system to determine if there is any leakage
  • When you detect the leak, use a Freon leak repair kit and follow the instructions to fix it. You can find the best Freon repair kits on Amazon. Our personal favorite is the Direct Inject Refrigerant Leak Sealer.
  • If the refrigerant continues to leak, have a mechanic look at the cooling system to find the problem.

Knocking Sound

If you notice a knocking or clicking sound when your car AC is on, the problem may be the mounting of a compressor part. Typically, the mounting bolts for these parts will be loose. To fix this problem;
Start the engine of your car

  • Open the hood and stand back to observe the cooling system
  • If the problem is the mounting bolts, you will notice the loose part shaking or moving around
  • To fix the problem, tighten the mounting bolts using the appropriately sized wrench and invest in a thread locking compound to help fix the problem permanently

Hissing Sound

In most cases, a hissing sound shouldn’t be a cause for alarm. The sound is caused by equalizing pressure due to the refrigerant moving from a high pressure side in your compressor to a low pressure side. You will normally hear this sound even after turning off the AC and the car.

In other cases, however, this may be an indication that there is something wrong with the compressor or the entire cooling system. The possible causes may be a leaky refrigerant line, an internal valve leak, or high pressure build up inside the compressor.

Therefore, if you hear an intense and prolonged hissing sound, chances are there’s something wrong with the compressor. Therefore, it is wise to call a mechanic as soon as possible.

Consistent Rattling Sound

A consistent rattling sound is a pretty good indicator that your AC compressor is about to be damaged. Many factors contribute to the damage of the compressor. It may be that the belt has worn out or the compressor clutch needs replacement.

Again, it is a good idea to have a mechanic check out the overall cooling system to correctly diagnose the problem – that’s the only solution on how to quiet a car AC compressor if it makes rattling noises.

Constant Vibration & Noise

If your compressor vibrates and makes noises consistently, it may simply mean that needs lubricating oil. The lack of lubrication is normally caused by leakage or low pressure in the compressor. To lubricate the compressor, follow these steps;

  • Purchase a good quality oil injector and refrigerant oil – our top picks are the Wisepick A/C AC Oil and Dye Injector and FJC PAG Oil.
  • Use a clear tubing to suck oil from its bottle without using your mouth
  • Once filled, jiggle its plunger to remove air bubbles
  • Start the car engine and put the AC on maximum cooling
  • Inject the oil into the cooling system (follow the manufacturer’s instructions on how much to add). Typically, half an ounce is enough.
  • As the system begins to run the oil, you will notice that the sound disappears


When you notice any sounds coming from your car AC compressor, it is always wise to take it seriously. It’s a good idea to equip yourself with even the basics of how to quiet a car AC compressor. It’s a great way to save cash as you will not have to spend hundreds of dollars on new compressors or detailed mechanical diagnosis. So take your time to learn these basics tips on how to quiet a car ac compressor.

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