Front ac blows cold but the back blows warm

What is your question?

Ac works fine. Fans blow strong both front vents and back but the back blows warm.

How long has your 2013 Ford Explorer had this problem?

Had an episode a month ago for a day. Then worked normal not having to do anything. Then today we turned on the back air and it blew warm.. Good strong flow, but warm.. kind of felt like it was trying to blow cool but went warm.