At 1439 Pacific time, the scheduled American Eagle flight encountered icing conditions during its en route climb at about 11,500 feet msl and departed controlled flight. Instrument conditions prevailed; none of the two flight crewmembers, one flight attendant and 25 passengers were injured. The crew recovered the airplane, continued to their scheduled destination and landed without further incident. As the airplane climbed through 11,000 feet msl, the captain noted light rime ice accumulating. The captain reached up to activate the manual deice boot system and the airplane vibrated. The airplane encountered ice and the windscreen immediately turned white. The clacker and stick-shaker activated, the captain took control of the airplane, the autopilot disengaged and the airplane began to bank to the left in a nose-low attitude. The airplane began a rapid descent and the captain recovered at an altitude of about 6500 feet msl. The day prior to incident a flight crew reported that during an en route deice boot check, the timer light illuminated. The deicer timer failure light was later deferred in accordance with the operators minimum equipment list. Initial examinations revealed the airplanes deice systems were operational; however, the deicer timer failure light illuminated.