Hi all,

I have a 2007 i6 HSE and when the air conditioner air temp is ambient to the outside air temp, it makes a slight whirring noise in tune with the revs of the engine, is this normal?

Last edited by freemander on 6th May 2014 11:19 am. Edited 1 time in total

Yep, normal and specific to the compressor of the petrol equipped cars.
It has to do with the compressor's internals.

Thanks for your reply, it's a strange noise, like the power steering pump is running dry but when you turn off the air conditioning, it goes away.

I have the same problem with mine, it can also be noisy when on econ mode. Its really annoying!

Must admit, the noise stops when switched to econ mode or if you change temp but agree it's annoying. It sounds like a power steering pump running dry

Mark1988, on the diesel model you have a different compressor and compressor on/off system.

On petrol model there is no on/off clutch. It has an internal valve for regulating the output.
It has to do with how the compressor regulates its output / displacement through its internal PWM regulated valve.
When near "no output" it gives that sound. This is when the temperatures have reached an equilibrium.
When you switch it off, it's obvious why you don't hear it.
When you modify the temperature, then it starts to put out some work and also you don't hear it.

The difference between diesel and petrol systems are somehow like the difference between household aircon systems: normal ones and inverter ones.
Normal ones regulate the temperature by periodically turning on and off the external/compressor unit. Meaning alternating between 0% and 100% output.
Inverter ones regulate the temperature by variation of the compressor output. The output can be any value between 0% and 100%. But the compressor is spinning all the time, it doesn't have on/off periods like the normal systems.