You probably have the basic 4 " fan in the opening . Just unscrew the handle and remove ,then take out the 4 screws that holds the cover on . There will be 2 screws that hold the screen on . You are then wide open to check the mechanism . I think it is held in with one screw/ bolt . All from the inside . Clean out spider webs while you are at it .
It was a rainy few days at Algonquin Prov park...tarps kept us dry.
Wayne --Belle River (Windsor), Ontario
2013 Sunset Trail Reserve 25RB..
2015 White Chev Silverado 2500HD 4x4 (6.0 l gasser)
2003 Mountain Star 890SBRX Truck Camper