King Air C90 flight crew reported elevator trim wheel stuck in the neutral position. Flight crew diverted and landed uneventfully.

Narrative

Aircraft departed ZZZ1 at XA:06 on Day 0. There was light to moderate rain and light turbulence on departure. Climbing through approximately 14;000ft; we began to pick up trace to light rime icing; and operated aircraft anti-ice systems. Passing FL200; all icing on the leading edges of the aircraft appeared to have sublimated off the aircraft. After leveling off at our cruise altitude at FL240; we noticed a yellow ELE trim annunciator on the G1000 PFD (Primary Flight Display) indicating an Autopilot mistrim. We followed the G1000 supplement elevator mistrim checklist and observed no change. When attempting to manually move the elevator trim wheel; it was found to be stuck in the neutral position. The aircraft was still easily controllable with pitch and power. Suspecting that the elevator trim system had iced up as we flew through the icing layer; we made the decision to descend to a lower altitude where the air temperature was substantially warmer. At the same time; we decided to divert to ZZZ which was only a few minutes flying time from our current position. As the aircraft descended through warmer air temperatures; we operated the elevator trim system; and it operated normally. The aircraft was landed without incident at ZZZ. Prior to flight; all preflight checks had been completed by the crew; including adjusting the elevator trim for takeoff.