2001 F250 AC/Heater mode door switch

Have a 01 F250 that the mode doors will not work between floor, center or defrost vent. It will almost always blow air through the defrost. for example for A/C it comes out the defrost vents even though it is switched to the center vents. Is this the controller or do you think it is actually the mode actuator on the A/C module? Is it expensive to replace either controller or actuator? Thanks for any help

im assuming the ac, check www.f150aftermarket.com (http://www.automotiveforums.com/vbulletin/www.f150aftermarket.com) for some cheap replacements