Engine vibration when A/C is on
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Thread: Engine vibration when A/C is on

  1. #1
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    Question Engine vibration when A/C is on

    Hello,

    I have 2015 Kia Optima with 2.0 Hyundai Nu Engine.

    When car is Idle and A/C is on, engine vibrates a bit. Not so much vibration but my old Toyota doesn't have that problem. Is that normal?

    I also noticed that RPM does not increase when A/C is on at idle. RPM is at about 650RPM to 700RPM at idle and A/C is on (and engine is already warm).

    A/C is cool though, doesn't have any problem. Just wondering if that is normal vibration and if RPM should increase when A/C is on?

    Thanks!

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  3. #2
    Senior Wrench Monkey
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    The A/C compressor is a variable displacement compressor, which means it's always operating and has no clutch to kick on and off. If you hear the engine change at idle, it's probably the cooling fan on/off operation, but the cooling fan creates quite a bit of force when operating, so maybe this is what you'll feeling/hearing and the RPM would remain normal.

    I would think that in your area the compressor would be the same as our US models, but we don't have Nu engines, but as yours was replaced because of no cooling at idle, a normal problem with the VDC. Actually the electronic control valve goes haywire in the back of the compressor.
    Last edited by Turbonut; 04-11-2019 at 07:43 AM.

  4. #3
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    Thanks @Turbonut! So I guess it is pretty normal vibration then. It doesn't bother much but I though it is worth asking.

    Service center said the problem is at what they called "Control Bar" which is attached in the compressor and they took it out to show me. They said that is usually the cause of the problem. But they replaced whole compressor just to make sure since it is still under warranty.

    I guess A/C compressor is common problem with KIA because I see quite alot of cars with A/C failing at service center everyday.

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  6. #4
    Senior Wrench Monkey
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    Actually a control valve, and yes common problem with Hyundai/Kia.
    Example:
    https://www.ebay.com/itm/FITS-2011-K...-/201991818300

  7. #5
    Riding Lawn Mower
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    2018 Optima EX
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    Quote Originally Posted by Turbonut View Post
    The A/C compressor is a variable displacement compressor, which means it's always operating and has no clutch to kick on and off. If you hear the engine change at idle, it's probably the cooling fan on/off operation, but the cooling fan creates quite a bit of force when operating, so maybe this is what you'll feeling/hearing and the RPM would remain normal.

    I would think that in your area the compressor would be the same as our US models, but we don't have Nu engines, but as yours was replaced because of no cooling at idle, a normal problem with the VDC. Actually the electronic control valve goes haywire in the back of the compressor.
    So if the compressor is always turning, how much drag is this putting on the engine when you don't have the A/C or defroster engaged?

  8. #6
    Senior Wrench Monkey
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    Not much drag at all. To simplify the internals, with no a/c called for, the direct drive compressor is just turning, virtually no drag, and when needed, the piston stroke becomes longer, but at highway speeds the compressor once again is just working easily.
    Take a look on the internet to get more familiar with the VDC.

  9. #7
    Newbie
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    It is actually quite interesting and good to understand how a part of your car works.


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