Noise under the hood when A/C is on

CRYSTALB47

MEMBER
2012 KIA FORTE
2WD
AUTOMATIC
136,000 MILES

Hi, I have noticed that my car makes a loud sound when my A/C is on and I am in drive or reverse. The sound isn’t there when the A/C is off and I’m driving the A/C blows cold air. When in park I can feel the vibrations of the knock when I turn the A/C on when I’m driving. Any help would be appreciated. Thank you.

6 Replies

JACOBANDNICKOLAS

MECHANIC
109,874 POSTS

Hi,

Can you describe the sound? Also, if possible, can you record it with your phone and upload it for me to hear?

It seems to be associated with the A/C compressor's engagement, but without hearing it or knowing what it sounds like, I'm not sure what we are dealing with.

Let me know. I need to know if it is a knock, squeal, vibration only, or however you would best describe it.

Joe

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Monday, July 20th, 2020 AT 4:17 PM

CRYSTALB47

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4 POSTS

I tried to record the sounds but the A/C is too loud. I can only hear it when I have it drive or reverse. I would describe it as a knock and a bit of vibration as well for example if I was at a stoplight and my foot was on the brake and the A/C was on I can feel the vibration in the brake pedal from the noise it makes.

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Monday, July 20th, 2020 AT 4:25 PM

CRYSTALB47

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4 POSTS

It is more like a rattling vibration but it gets aggressive.

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Monday, July 20th, 2020 AT 4:25 PM

JACOBANDNICKOLAS

MECHANIC
109,874 POSTS

Hi,

Okay. Does the vehicle have a tachometer? If it does, I need you to pay attention when you turn the A/C on to see how low the RPM's go. Let me know what the idle speed is without the A/C and with. There is a device on the engine that is to compensate for the added load from the A/C. If it doesn't, the RPM's may be getting too low and causing a vibration felt throughout the vehicle.

Do that and let me know.

Joe

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Monday, July 20th, 2020 AT 6:22 PM

CRYSTALB47

MEMBER
4 POSTS

Hi, I was finally able to reviews the sound a bit I’ll attach a a video. That’s A/C blows very cold and the noise only happens when the car is in gear but not when driving.