I have noticed on my 07 that if I am using either of the two defrost settings that my AC light comes on and can't be turned off. Anyone know why this would be?

 

Because that's how it works. The ac system removes moisture from the air. You have fog on your winshield because there is moisture there.

 

My 00 does this too,,, it's to remove the interior moister,, (just like your home AC de-humidifies) Although on mine, I can turn it off,,, there was a post that told you how to disable that function, by going through a process of pushing and holding a certain button,,, Also, alot of cars will also switch the air intake to the outside air,, versus the re-circ,,,

 

you can reprogram it so u can manually turn it off. is what i did.. you dont always have to have a/c to defrost.. and somethings like that justing using the defrost settings for my normal air minus the a/c

found this somewhere

To deactivate automatic a/c feature on a 2002+ S2000:

1) Turn the ignition switch "on," but dont start the car.
2) Turn fan speed off.
3) Turn temperature knob all the way to the left (blue area).
4) Turn vent knob to all the way to the left (panel position).
5) Turn the ignitions switch "off."
6) Hold down both air recirculation button and a/c button while turning the ignition switch "on." Nothing lights up initially, keep waiting. The orange air recirculation indicator on the button will start flashing.
7) Continue holding both buttons until the orange air recirculation indicator stops flashing, then let go.

 

i have it set so the AC goes on automatically when i turn on the defrost, but i can immediately turn the AC off and leave the air coming through the windshield vents.

i believe i followed these instructions-

To deactivate automatic a/c feature:

1) Turn vehicle off.
2) Turn fan knob off.
3) Turn temperature knob all the way to the left (blue area).
4) Turn vent knob to panel only setting.
5) Hold down both air recirculation button and a/c button while starting car.
6) Continue holding for 7 seconds until air recirculation button stops flashing.

**edit**

oops i was too slow.

 

thanks all.