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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Gustavo

17 years of experience
368 reviews
Gustavo
17 years of experience
Ford Escape L4-2.5L - AC is not working - San Antonio, Texas
Super professional & timely! Knows his stuff! Second time using him for my vehicle will definitely keep selecting him when going thru “your mechanic”
Honda Accord - AC is not working - San Antonio, Texas
Gustavo solved a problem the Honda dealership missed. He was accommodating and explained everything clearly. 

Brian

23 years of experience
612 reviews
Brian
23 years of experience
Nissan Maxima V6-3.5L - AC is not working - Jacksonville, Florida
Brian was very thorough and informative. He answered all my inquires about my vehicle. Thanks for the fine service. Ronald Young
Kia Rio - AC is not working - Jacksonville, Florida
Brian was professional and very knowledgeable, he had answers for the issues related to the A/C that may (or may not) have been the root cause for the system not working properly. I would recommend Brian.

Jay

37 years of experience
910 reviews
Jay
37 years of experience
Chrysler Town & Country V6-3.3L - AC is not working - Chino, California
Timely arrival, clear communication on the problem, he did everything he could to correct it and told us the likely developments. We needed a quote for possible next steps and he provided that immediately. Assisted us in setting up the follow up appointment.
Mazda MX-5 Miata - AC is not working - Hemet, California
Great Guy and Mechanic, he knows hi stuff. He was clean, efficient and knowledgeable. When he finishes with the current job, I am having look at replacing the brakes on my truck!

John

27 years of experience
951 reviews
John
27 years of experience
Nissan Rogue Sport L4-2.0L - 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!!
Ford Transit-350 - AC is not working - Friendswood, Texas
Our second time using John to work on the van has made it clear - if he can perform the necessary work, we will never go to anyone else. Fixed the AC in my van for much less than I would have paid at the dealer. The best mechanic we have ever used: honest, friendly, goes above and beyond, and never offers extra services. He had to buy some extra supplies this time around and didn't even charge us for them. We'll be having him back for our oil changes soon, and anything else that comes up before then!

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