2004 Ford Freestar Serpentine Belt?

Some are actually spring loaded and others just have a slot that allows for adjustment. Either one of those types should be visibly different.
If the belt is not used for cam timing, the adjustment may be done with one of the accessory items such as AC compressor, the alternator or the power steering pump. In this case, the adjustable device will have one pivot bolt and another that goes through a slotted area to allow the device to 'swing' for adjustment.
The pivot bolt should be only a little loose so one can just barely move the adjustable device, while the adjustment bolt should be free while adjusting. This may help not losing the adjustment after having set the belt tension correctly.