What is the difference between the 3rd and 4th modes, from left to right.

Supposedly the 3rd one is for when the top is down, and the 4th one for just the bottom fan.

However, to me it seems the same: the 3rd one just turns on the bottom fans, and turns off the top fans. Just like the 4th mode.

 

on MY01 the 3rd from left turns on the vents just above the radio. whereas the 4th one just does the lower fan

 

1----three big front vents. 2----same as 1 but adds the floor. 3----light on center big vent but same as 1 with two outside big vents, adds the above radio vents and also keeps floor. 4----floor vents only. 5----same as 2 but also adds the a-pillar vents and the windshield vents. 6----only the windshield vents and the a-pillar vents. i just went out 2 my S and checked it out. haha!

 

See page 97:
http://techinfo.honda.com/rjanisis/p.../AS20808OM.pdf