Belt got shredded, as in it was coming off in strands while driving. Replaced the Serpentine belt and now when the key is turned the pulleys will try to turn and the belt moves a little but won’t go over completely. Take the belt off and it starts and runs fine. Know for sure the belt is put on the right way, any idea what could be causing that?
Are you absolutely sure you’ve got the correct belt for your application . . . there at least 2, maybe even 3, different engines offered for the Ranger during that model year
Another possibility, considering the engine starts fine with no belt . . . one of the accessories (water pump, alternator, power steering pump, etc.) is seized or otherwise damaged
In spite of the fact that the pulley is supposed to freewheel with a frozen ac compressor, we have several Fords in our fleet, where it didn’t work out that way. The ac compressor bit the dust, then proceeded to shred and eventually throw the belt. The compressors looked strikingly similar to the one used for that 2007 Ranger. Same ac compressor manufacturer, presumably
I seem to recall some issues with Ford AC compressor hub bearings of that period now that you mention it. That’s a likely possibility for the OP’s problem.
I think the OP was describing the little bit of movement in the new belt that occurred as the starter motor tried to turn the crankshaft while it was being held fast by the frozen component.