Dear Micky:
regarding autopilot OFF in icing conditions. While you should certainly consult the aircraft manual, the idea is this:
if you tell the autopilot to maintain altitude or rate of climb etc, the autopilot is not really holding altitude, it is TRYING to hold altitude my manipulating the elevator.
if the wing gets iced up, the autopilot will have to work harder and harder to hold altitude UNTIL the elevator makes the wing get to critical angle of attack ( in England it is known as angle of incidence) and the wing stalls. now the plane is losing altitude and the dumb autopilot either disengages or continues to pull "up" on the elevator taking you deeper and deeper into the stall.
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A human pilot would say: hmmmm, the plane is getting harder to handle, oops I can't hold altitude, better to trade altitude to get out of the stall and regain control especially with the wing's efficency compromised by ICE.
a tragic crash happened in America, near chicago when an ATR72 iced up on autopilot and spun out of control killing all aboard. YOU , as the pilot, must ask yourself ,'is it better to lose altitude and make a semi controlled crash landing (or better yet, escape the ice) and survive or watch the autopilot pull up and up till control is lost?"
please let me know if you understand this and be sure to check with YOUR flight instructor before you go charging off into the great unknown.
regards
jon