C182 Captain reported autopilot failure resulted in momentary loss of control and an expeditious return to a safe landing.

Narrative

Departure from ZZZ on vectors; engaged autopilot at 4;200 experienced unexpected partial failure of Century 2000 'autopilot' in climb mode resulting in erratic maneuvers to regain control of aircraft (aggressive left bank and loss of 1000 ft MSL... Actions to immediately turn off autopilot stopping banking and runaway electric trim from climb setting to a aggressive decent (1500 ft/min). Overcoming radical trim set and in process of returning to course control achieved. Tested autopilot momentarily with immediate complete failure requiring further irratic maneuvers but PIC regained control... ATC contacted aircraft several times during incident procedures and gave priority handling on our behalf. Vectored and altitude clearances provided partial VFR flight while returning to ZZZ. Landed and returned to maintenance FBO where the equipment was reviewed by multiple staff and A&P personnel.Findings included validation of unit failure; flown up to the FBO in City X also confirmed unit failure and known history of other customers with similar incidents.Action plan: unit replacement...