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Vibration When The Air Conditioning Is On

Stronger vibration at idle when the air conditioning is switched on usually means the engine struggles with the extra load: worn engine mounts, a low idle or a dirty throttle body are common causes.

Normal risk

Usually not urgent. Have it checked if the engine almost stalls or the vibration is severe.

Short answer · Why does my car shake when I turn on the AC?

The AC compressor takes power from the engine. The engine control unit should raise the idle slightly to compensate. If the idle stays too low, the throttle body is dirty or the engine misfires, the engine shakes. Worn engine mounts pass this shaking into the cabin. A compressor that is failing can also add vibration.

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Safe checks you can do

  1. Watch the rev counterThe idle should rise slightly or stay steady when the AC switches on.
  2. Compare with the AC offIf the vibration disappears, the extra load is the trigger.
  3. Check for warning lightsAn engine light points to idle control or misfire.

Questions that narrow it down

  1. Does the idle drop a lot?Idle control or a dirty throttle body.
  2. Is there a noise from the compressor?The compressor may be failing.
  3. Is the vibration also there in drive at a stop?Engine mounts are likely.

Possible causes

Listed without ranking. Use the questions above to see which ones fit your car.

  1. Worn engine mountsPass vibration into the cabin.
  2. Low idle speedEngine runs too slowly under load.
  3. Dirty throttle bodyPoor idle control.
  4. MisfireRough running gets worse under load.
  5. Failing AC compressorAdds load and noise.

Questions about Vibration When The Air Conditioning Is On

Can cleaning the throttle body help?

On many cars it improves idle stability. Some need a relearn procedure afterwards.

Is it bad for the engine?

The vibration itself is not dangerous, but the cause should be fixed.