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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Jeremy

20 years of experience
436 reviews
Jeremy
20 years of experience
Toyota Tundra - AC is not working - West Palm Beach, Florida
Jeremy was awesome. What a great experience. I will definitely use this service again. Thank you so much
Dodge Grand Caravan - AC is not working - Boynton Beach, Florida
Jeremy is a very nice guy, immediately gets to work and resolve the issues. This is the second time he’s worked on vehicles for me and each time was an excellent experience. Highly recommend him

Peter

25 years of experience
430 reviews
Peter
25 years of experience
Scion xA - AC is not working Inspection - West Hills, California
Peter has an awesome personality. Very knowledgeable and friendly. Definitely no BS from him. Very honest.... Will I use him again? Definitely. Will I refer him? Absolutely! Thank you Peter!
Mercedes-Benz ML500 - AC is not working Inspection - Reseda, California
Peter took his Time to check out and diagnose my vehicles problem. I was able to add some Freon and the cooling system is most definitely getting colder. I’m gonna drive it for the next few days as recommended and see where I’m at and go from there. Thank you for your time Peter

Matthew

33 years of experience
1017 reviews
Matthew
33 years of experience
Acura RDX - AC is not working - Newport News, Virginia
Matt is always so pleasant to work with. I appreciate his knowledge and attention to detail with my car. Thank you Matt!
Chevrolet Impala - AC is not working - Newport News, Virginia
Matt was on time and during the discussion with him he showed a great deal of knowledge about my a/c issue. I book this repair this weekend and look forward to Matt repairing my car. Thank you Matt

Bryant

12 years of experience
509 reviews
Bryant
12 years of experience
Jeep Patriot - AC is not working - Indianapolis, Indiana
Always great service with Bryant, he explains all he is doing as well as what else needs to be complete. I will be scheduling my next visit from him soon.
Ford Expedition - AC is not working - Indianapolis, Indiana
Second time using Bryant and he was, in both instances, able to diagnose and locate the problem. What I find particularly great is that both issues were very easy and inexpensive fixes. Bryant was very candid about the problem and offered to show me how to fix the issue if I wanted to do it myself. I just had him make the repair, which was done quickly. He also found an alternative part that saved me from having to order it online and wait a few days for the repair to be made. Bottom line, Bryant does what’s right and is honest about what the problem is. Anyone could have told me its a $1,200 repair and I wouldn’t have known differently. Use Bryant if you want honesty and great work.

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