THCROZIER... in answer to your Q
The advice in icing is to disengage auto-pilot. A/P will disguise subtle 'feel-back' to a pilot that otherwise would warn him of unnatural trim settings.. in a worst case scenario the A/P will ultimately give up trying to compensate for extreme trim settings and disengage itself leaving the pilot to cope with a hopelessly out of trim and possibly unrecoverable aircraft flight attitude. When a/c flight characteristics are steadily deteriorating due to steady ice build up (extra weight/ increasing angles of attack / disrupted airflow over critical lift surfaces and possibly under extreme conditions on some aircraft, less power available) it's far better for the pilot and a/c to be in touch with each other....