What was found
DURING A ROUTINE FLIGHT FROM KPSM TO KBTV, THE CREW EXPERIENCED DURING CLIMB THE YAW DAMP WOULD NOT ENGAGE. ON THE THIRD ATTEMPT TO ENGAGE THE YAW DAMP, AP FAIL CAS MESSAGE FOLLOWED 2 SECONDS LATER BY A RED TRIM RUNAWAY CAS. AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO KPSM WHERE THERE WAS AN UNEVENTFUL LANDING. TECHNICIANS REMOVED AND REPLACED THE YAW TRIM ADAPTER SSSD RELAY A262K4 IAW WDG 91-10-08. PERFORMED A/P ADJ/TEST IAW AMM-12-C-22-10-00-00A-903A-A WITH NO DEFECTS.