Q:

Is it normal for an AC pump to wait for a second before starting to turn?

I have a diesel Laguna 08. It has been giving a little bit of extra noise from the engine lately. I have noticed the one of the pulleys on the belt does not start like the others when the belt starts turning. This is the lowest one down in the engine and from looking at pictures it seems to be the AC pump. 
This extra bit of noise I mentioned also has a delay to it and the noise seems to start at the same time that this pulley starts to turn — so my theory is that maybe there's a worn out bearing or something on the AC pump ( or it might be the power steering pump I suppose) 
... but amidst all this I'm puzzled about why it has a delay to it - which means the belt is running over the pulley so the pulley is not turning for the first second or two after engine start. 
This is my question - is this normal and if so why, and if not would it be a major issue. I was thinking that I'm not too worried if the AC pump bearings are starting to go I will just wait until it fails to replace it but now I'm not so sure.

A:

The A/C compressor has a clutch mechanism that allows the compressor to be turned on and off.  It is therefore normal to see the belt turning without the compressor running.
When the A/C computer wants the compressor to run, it sends an electrical signal to the compressor which operates the clutch.  You should be able to hear a click as the clutch is operated.
If you watch this video @ 1 minute in, for example, you will see the disengaged clutch stationary while the pulley is turning.

