Odd heat vent symptoms
 

I've got a 2010 Insight EX with about 85K on the odometer. Lately I've noticed something weird with the dash vents. Three or the four will be feeding cool air and the fourth hot. The problem vent is the one at far left, blowing on the drivers left arm. Does anyone now why the temperature would be different on different vents, and why the one would consistently blow warm? I've got climate control set to auto...