I have a 2011 S650 and the Over head air ducts are not blowing anything at all. The vents by my knee seem to have good flow but the ones above are dead. I have checked the outside air filter (still not sure where the in cab filter is or how to get to it). I assume a duct has come loose or they are stopped up. What is the best method to go about diagnosing the problem and then what would be the best solution? Thanks!