Some 2011 models had a problem with the Blend Door Actuator sticking. There is a TSB on it in the 'Sticky' section. It is shown as TSB 12-1-8 DUAL AUTOMATIC TEMPERATURE CONTROL (DATC) - BLEND DOOR ACTUATOR INOPERATIVE.
Not sure if that might be the issue.
Also, please add the model of your Explorer to your profile so that it shows in the margin when you post and we will know which one you are referring to.
Peter