A Jeep window regulator most often breaks from a snapped or frayed cable, stripped internal gears, a cracked plastic window carrier, or repeated strain from a window that's binding somewhere in its track. Cold weather can also make an already-worn regulator more likely to fail, since stiff, brittle parts handle sudden movement worse than warmed-up parts.
Cable-style regulators rely on a thin steel cable wound around a drum or pulley system to raise and lower the window. That cable is under constant tension every time the window moves, and, like any cable that flexes repeatedly, it eventually frays at a pulley or anchor point and snaps, usually with little warning beyond a bit of extra noise beforehand.
The plastic components inside a regulator are just as important as the cable itself. The carrier that clips onto the bottom of the glass, along with various small guides and clips throughout the mechanism, is typically made of plastic that becomes more brittle as it ages and cycles through Ann Arbor's seasonal temperature swings. A carrier that cracks can let the window tilt in its track or drop unevenly, which puts uneven strain on the rest of the regulator.
A window that's binding for any reason, whether from a dirty or damaged track, a door that's slightly out of alignment, or debris that's worked its way into the channel, forces the regulator and motor to work harder every time you use it. That extra strain wears down gears and cables far faster than normal use would, which is why a regulator that fails early in a vehicle's life often has a mechanical cause elsewhere in the door rather than a defective part.
If your Jeep's window is moving slower than usual, sagging to one side, or making noise when it goes up or down, it's worth having it checked before the regulator fails. Hoover Street Auto Repair in Ann Arbor can find out exactly what's wearing out on the regulator and fix the underlying cause as well.