Knocking sound when A/C turned on

2000 INFINITI I30
145,000 MILES • 2WD • AUTOMATIC
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CHARLESTUCK
  • MEMBER
  • 66 POSTS
It stops when the air conditioner is turned off. The knocking sound is a heavy sound like crank bearing noise. Has made the sound while accelerating from start on incline. 180,000 miles.
Aug 21, 2018 at 9:20 PM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
Hi and thanks for using 2CarPros.com.

If it is only happening when the AC is turned on, chances are the compressor is bad or going bad. Using an automotive stethoscope, listen the AC compressor to determine if that is where the sound is coming from. Be careful because the engine will be running, the belt turning, and the compressor engaging.

If you do not feel that is the problem, check through this link and see if there is anything that helps. If there is not let me know and we'll continue checking.

https://www.2carpros.com/articles/engine-noises

Take care,
Joe
Aug 22, 2018 at 11:15 AM
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CHARLESTUCK
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  • 66 POSTS
Thanks Joe.
Aug 22, 2018 at 11:21 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
I hope what I suggested helps. Let me know if you need anything or just have other questions.

Take care,
Joe
Aug 22, 2018 at 12:18 PM
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ASEMASTER6371
  • ✓Experienced Mechanic
  • 52,796 POSTS
Good afternoon.

It sounds like you have a failed AC compressor. There may be a failure internally causing the knocking noise. Make sure the belt is good and tight as well. A faulty tension-er could also cause the issue.

Roy

https://www.2carpros.com/articles/replace-air-conditioner-compressor
Aug 24, 2018 at 4:48 AM (Merged)
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CHARLESTUCK
  • MEMBER
  • 66 POSTS
What accounts for the noise when the A/C compressor is not switched on such as the time when the car was started and driven from an incline (A/C off)? Also, why does the noise not occur when on highway with the A/C switched on? Thanks.
Aug 24, 2018 at 4:48 AM (Merged)
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ASEMASTER6371
  • ✓Experienced Mechanic
  • 52,796 POSTS
I would start by having the belt, tension-er and front bearing checked. That may be the entire issue.

Roy
Aug 24, 2018 at 4:48 AM (Merged)
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