Here it is:
- Have the car turned off.
- Turn the "air condition position" knob to the left all the way (counter-clock-wise).
- Hold the "air-recirculation button" and the "A/C" button "DOWN". (don't touch the "defrost" button)
- Start the car with the "BUTTONS" held down, and wait for 7 seconds. (The recirculation light will flash, keep holding down the buttons till the A/C light comes on.)
- Turn the car off then back on.
Now you can turn the "A/C" off and on now with the defroster setting selected.
Source:
DIY: Shutting of A/C during defrost [Archive] - 7th Gen Honda Forum - The #1 Community for 2001-2005 Honda Civic Enthusiasts