When I turn on the aircon and fan a high pitched squeak occurs like a slipping belt, but only when the aircon is on.... any thoughts? Cheers

 

Could be the compressor belt.

 

Try some belt dressing. It is cheap and simple

 

If it still has low mileage on it you shouldn't need to use belt dressing. Look at the serpentine belt and see what the condition is. Are all of the teeth in good shape and is the surface soft and pliable (not glazed over.)

I haven't looked at my car to see if it has an idler pulley or if you set the belt tension with the alternator, but if there is an idler pulley, make sure that is exerting a decent amount of force on the belt to keep it tight (I've had the spring inside the idler pulley break on another vehicle, but at ~60,000 miles) If the alternator is used for tension (mounts on a pivot and is rotated tight), then just make sure the belt is tight but not rigid.