Citationjet (C525/C526) - CJ I / II / III / IV
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 86; Flight Crew Total 3070; Flight Crew Type 626
Troubleshooting; Workload
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Aircraft Equipment Problem Dissipated; Flight Crew FLC Overrode Automation; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Regained Aircraft Control
Aircraft
Upon starting descent from 39;000 MSL the amber boxed auto pilot out of trim box appeared on both PFDs. After reviewing the abnormal checklist; I disconnected the auto pilot and the aircraft made an uncommanded pitch up.Next; I discovered the pitch trim wheel was frozen and unable to be moved up or down with manual or electric trim. Both with the electric trim breaker pulled or without. I was able to maintain positive control of the aircraft using heavy forward pressure on the control yoke except for the brief moment when the auto pilot disconnected and did not deviate from ATC instructions. Therefore; I felt no need to declare an emergency at the time of the event.Upon reaching warmer air; around 11;000 MSL the pitch trim freed up. A normal descent and landing at our destination airport followed.
Reporter stated aircraft actuator was lubed and flown at low altitude with no issues. At high altitude; same control issue was present. The reporter heard water was found in the actuator from a second hand source.
CE-525 Captain reported the elevator trim control froze at 39;000 feet then descending to warmer air to thaw it.