What was found
(CAN) PILOT ATTEMPTED TO TRIM ACFT ON CLIMB OUT USING ELECTRIC TRIM TO LEVEL OFF FOR TRAFFIC AVOIDANCE. ACFT FAILED TO RESPOND. EVASIVE ACTION TAKEN AS REQUIRED. FLIGHT CONTINUED USING COPILOT TRIM SWITCH AND/OR MANUAL TRIM AS REQUIRED. ON GROUND PILOT ATTEMPTED TO TROUBLESHOOT PROBLEM. HALF OF THE TRIM SWITCH ACTUATOR (ONE SIDE OF THE 2 PART ACTUATOR) FELL OFF WHEN VERY LIGHT PRESSURE APPLIED TO MOVE THE SWITCH. BOTH SIDES OF SWITCH MUST ACTIVATE FOR TRIM TO MOVE. NEW SWITCH INSTALLED AND ACFT RETURNED TO SERVICE. (TC 20100223003)