Self-Diagnosing Weird Car Air Conditioner Noises

January 7, 2018

These five noises coming from your car’s AC could signal trouble or be totally normal. See which sounds you’ll need to have checked by a mechanic before they get worse.

Is your car’s air conditioner making weird noises?

While your AC should normally run cool and silent, you may have a problem on your hands if certain strange sounds are left unchecked.

Before you unknowingly cause greater damage (and more expensive repairs), see if one of these car air conditioner noises sounds like what you’re hearing — and find out what it means.

How To Diagnose 5 Weird Car Air Conditioner Noises Before You Visit a Mechanic

These are the five most common car air conditioner noises drivers report to their mechanics during service:

#1. A Loud, Squealing or Screeching AC Sound


Loud squealing or screeching is the most common noise drivers experience when they turn on a malfunctioning AC.

This sound often signals an issue with your drive belt or serpentine belt.

The serpentine belt is responsible for turning the pulley at your air conditioner compressor, which pressurizes the refrigerant lines and makes it possible for cool air to reach your cabin, among other duties.

Though squealing or screeching is a good indicator of a worn belt needing attention, you can examine your serpentine belt for signs of wear like cracks and tears, or missing ribs facing the pulley, before you bring your car in for service.

You’ll still want a mechanic to diagnose the issue definitively because failing bearings in the compressor pulley can also make noises like squealing, roaring, and grinding too.

This next car air conditioner noise is also very common — but not necessarily bad.

#2. AC Hissing When the Car Shuts Off


A hissing noise is another common sound drivers hear from their car’s air conditioner. The good news is this doesn’t always spell trouble.

If you hear the AC hissing after you turn your car off, that’s actually just your car’s way of equalizing pressure.

See, there’s both a high pressure side and a low pressure side in your system when the AC is running. A refrigerant like Freon moves between these two separate sides which are divided by either an expansion valve or an orifice tube.

Turning off your car will cause the Freon to move from the high-pressure part of your AC compressor down to the side with lower pressure to equalize out.

While AC pump noise is totally normal for your car’s air conditioner, hissing at any other point may give you reason to visit your mechanic, just like a buzzing noise.

Car Air Conditioner Noises

#3. AC Buzzing Noise

If you’re hearing a car AC compressor noise while accelerating, or a buzzing noise when you first turn on your car’s air conditioner, you may have too much Freon in your system.

Often topped off during a routine service visit, an overcharged air conditioner means the refrigerant may be entering your AC compressor intake port — and that’s bad.

Your AC will not be able to properly cool your vehicle and it may cause serious damage to your compressor or other components. Get your vehicle checked out ASAP.

#4. AC Knocking or Clicking

Hearing a knocking or clicking noise in car air conditioner is actually one of the easier sounds to fix on your own.

Knocking or clicking usually signals loose mounting bolts or any of the other various air conditioning components not being tight enough. The loose parts will rattle and shake and you’ll hear a racket when you kick on the AC.

To troubleshoot this issue, turn your engine on, pop open the hood, and crank up the AC. Check to see which parts are shaking and then tighten those so they stop. You’ll also want to add thread-locking compound to the parts to prevent them from loosening in the future.

This final noise may be the most serious to watch out for.

#5. AC Rattling

Your engine is under a heavier load when you run the AC. That means rattles can stem from any number of issues like a bad catalytic converter to a failing power steering pump pulley.

So if you turn on your AC and hear a rattle, it may mean you have a failing or bad:

AC compressor. Rattling or your car air conditioner making loud humming noises which get worse as you accelerate can both be signs you need to replace your AC compressor.

Compressor clutch. This high-wear part often needs replacing, especially if you live somewhere where you’re constantly running your car’s AC.

The compressor clutch pressurizes your AC and pumps refrigerant through the system. A rattling could indicate it’s time to replace your worn out compressor clutch (and maybe even the entire AC compressor).

Idler pulley. An air conditioner pulley making noise can also come from failing bearings. These typically start when your AC compressor engages.

If you think any of these issues may be causing your weird car air conditioner noises, it’s in your best interest to take your vehicle to a trusted mechanic where they can properly diagnose the real cause and fix it before you damage your vehicle any further.

Make an appointment today with the experts at Palm Beach Garage by calling 561-833-6622 now.