What was found
DURING CRUISE FLIGHT AT FL 360 WE PERFORMED APU CHECK AS APU CAME UP THE AUTO PILOT DISCONNECTED. RED A.P. DISCONNECT & SIREN RE-ENGAGED A.P., A.P. WAS NORMAL AT APPROX 26,000' WE GOT YELLOW AUTOPILOT DISCONNECT AND AUTOPILOT SISCRETE LITE. FULLY DISENGAGED A.P. CONTROLS WERE VERY HEAVY AND SLOW TO RESPOND. EMERGENCY DECLARED. GOT DELAYING VECTORS FOR ANOTHER APPROACH. LANDED SUCCESSFULLY WE GOT NO OTHER EICAS MESSAGES OR DISCRETE LITES. * LANDED IN SEA MTX GROUNDED AC AND DEFERRED CENTER AUTO PILOT IAW MEL ABX-22-10-1A AND RETURNED AC TO SERVICE .