The fan is supposed to spin free when its cold and the fan has a thermostatic coil that senses heat and causes the clutch to operate when the clutch gets heat blown at it from the hot radiator.
When the clutch is bad it either wont turn fast enough or is in a locked position that makes your car sound like a jet taking off.
1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T