2006 Civic EX - Low Air Flow
 

I just bought an 06 Honda Civic EX (US model with knob to control blower motor, and buttons to change vents). The heating/AC vents are blowing very little (almost none) air, even when the knob is turned to high. I can hear that the blower motor is spinning fast. I just replaced the cabin filter. It seems that the air is being redirected to the different vents as it should, when I push the buttons. I am very mechanical and have worked on cars a lot. But, heating/AC is one of those areas that I do not have a lot of experience with. Where do I start with this problem?