Why Does My AC Rattle When I Turn It On?

Your car’s AC system is designed to keep you cool and comfortable when temperatures rise. It’s designed to operate quietly and unobtrusively, so there should be little to no noise from an air conditioning system that’s in good working order. However, if you hear a rattle when you turn the air conditioning on, it could be any number of different problems.

While your air conditioner is technically a separate system, it’s tied to the rest of the engine by the serpentine belt. The serpentine belt is what’s responsible for turning the pulley at the AC compressor, and pressurizing the refrigerant lines. The compressor engages/disengages by an electromagnetic clutch.

If you turn on the AC and immediately hear a rattling noise, there are a few potential causes:

  • Compressor: If your AC compressor is beginning to fail, it can make a rattling noise.

  • Pulley: If the compressor pulley bearings are failing, they can make noises, generally a grinding, roaring or squealing noise.

  • Belt: If the serpentine belt is worn, it can slip when the compressor engages, causing noises.

  • Idler Pulley: It’s possible that the noise is actually from the idler pulley if its bearings are failing. The noise would start when the compressor engages due to the increased load on the engine.

  • Compressor Clutch: The compressor clutch is a high-wear item, and if it’s worn out, it can create a rattle during operation. Some vehicles can have only the clutch replaced, but some require replacement of both the clutch and compressor.

There are many other potential sources of the noise as well. When the AC turns on, it puts the entire engine under a heavier load. This increased load can cause rattles from things like the power steering pump pulley, loose parts (even a loose hood prop rod can rattle under th additional vibrations created by operating your air conditioner). If you hear a rattle in your car, have a mobile technician from YourMechanic inspect the cause of the sound.


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Greg

22 years of experience
333 reviews
Greg
22 years of experience
Toyota Corolla L4-1.8L - AC is not working - San Tan Valley, Arizona
Greg was very knowledgeable and shared all of the information and recommendations for my vehicle. He is personable and does a great job. Thank you Greg!
Nissan Rogue - AC is not working - Surprise, Arizona
Very happy Greg was able to come back, since he originally installed my compressor. He's honest, forthcoming, and explains exactly what he checks.and exactly what he does! I'm pleased yet again with my appointment! AND I have a/c again! Thanks so much!

John

27 years of experience
1019 reviews
John
27 years of experience
Kia Forte L4-2.0L - AC is not working - Houston, Texas
I really like this guy. He was direct, straight to the point & fairly honest about other things I already knew what was wrong with my car. I honestly felt like I could actually trust and believe In the guys integrity.
Nissan Rogue Sport - AC is not working - League City, Texas
Quick, efficient, detailed, professional. Everything you’re looking for in a mechanic! HIGHLY recommend him. Thank you so much!!

Benji

22 years of experience
277 reviews
Benji
22 years of experience
Honda Accord L4-2.4L - AC is not working - Phoenix, Arizona
Benji was running behind on his appointments. He called to give me very early notice to plan accordingly since he was 20 minutes behind. He's super friendly, knowledgeable, and a pleasure to work it. I would work with Benji again for my auto needs and recommend him to people I know.
GMC Yukon - AC is not working - Chandler, Arizona
On time, friendly, and professional. Gave thorough explanation of findings and answered all my questions - I would not hesitate in recommending Benji to anyone.

Peter

25 years of experience
514 reviews
Peter
25 years of experience
Toyota Matrix L4-1.8L - AC is not working - Los Angeles, California
Peter was incredibly detailed and was able to diagnose and fix my AC issue. As a new car owner, 10/10 I would hire Peter again to help diagnose and fix the issues on my Toyota. Thank you!!!
Ford Taurus - AC is not working - Granada Hills, California
Great experience! Peter lives close by and contact me to see if he could come by a day early at the end of his day. He made the repair, gave me instructions on what to look for in the future and all took 30 minutes.

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