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Car: BMW 2007 530i (N52 Engine) 210,000KM

Details:

  • Single accessory belt for AC, Power Steering, Alternator
  • AC is clutchless variable displacement
  • Tensioner and idler pulley's replaced

Problem:

  • There is a groan in the cabin when the AC is turned on
  • The groan is exacerbated when there is load on the steering wheel while turning
  • The groan disappears when the AC is turned off
  • The groan is there when engine is cold, regardless if AC is on or off

What I've checked:

  • No play in the pulleys for any accessory
  • No groaning noise in the engine bay
  • AC performance is good
  • Power Steering performance is good
  • Power Steering fluid has been flushed

The groan sounds like a power steering groan (especially when low on fluid) from my previous experiences. However, what's throwing me off is the noise is only there when the AC is running. Can the load of an AC cause another accessory to show symptoms?

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    The AC being on will definitely change the tension in the accessory belt. So my first thought is that the power steering pump is failing. Something like the bearing that is relatively quiet until the load changes due to the AC coming on.
    – jwh20
    Commented Nov 17, 2021 at 13:06
  • That's an answer @jwh20
    – GdD
    Commented Nov 18, 2021 at 8:38

2 Answers 2

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According to @Kaka_oyoo on Twitter, these are some possible causes;

  1. Low level of power steering fluid.
  2. Worn bearings on any of the peripheral devices driven by the serpentine belt, namely alternators, power steering pump, water pump, or air conditioning compressor.
  3. Worn serpentine belt.
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  • Who is "@Kaka-ooyoo on Twitter," and why should we think their view is accurate? Commented Nov 18, 2021 at 19:57
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YES! The A/C demands horsepower from the motor when the clutch is engaged for it. The power steering pump is nearly always these days on the same serpentine belt and the action of the lock in of the A/C stretches on the belt. If you have an older belt it may look fine but they don't always show an issue when stretched. All serpentine belts are designed to feel very tight from pully to pully with many so tight in a section a sound can be heard if you thump it like a loose drum head.

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