Is there only one Air mix mode actuator?

The heat/ac only comes out of the front vents no matter what position the control nob is on (defrost, floor, etc). At first it would change but sounded like something, a damper, was sticking. Now the **** just turns but doesnt change where the air comes out. I replaced the air mix actuator located behind the glove box but that wasn't it. The ford shop said there are several located behind the dash but everything I have looked up online always refers to only one. Am I on the right track? And how can I figure out which one needs replaced? I'm trying to repair on my own since no one can give me an estimate b/c it involves tearing out the dash. Thanks