Where's the idle wheel located? on 2004 Mercury Mountaineer

About two months ago, I started hearing this winding noise while driving. whenever I turn the air condition on and get at a certain speed.

Asked by for the 2004 Mercury Mountaineer
I think that you mean the fan belt Idler Pulley (wheel) and/or tensioner. These do wear out on Fords:
here is a good source of repair information for your car

this should help you with the needed to replace those components.