I have an issue with my cold air return. I don't think it's working (or at least isn't working right). My air conditioning seems to run constantly in the summer, yet the house doesn't seem cool. The cold air return is upstairs, in a hallway with 3 bedrooms and a bathroom off it. When I put a tissue near the return and there was no air movement. How can I see what's wrong or who to call to fix it?