Your ECONO button is essentially your AutoStop on-off switch and becomes active whenever your blower selector is not OFF.

By default your AC compressor always comes ON when you select DEFROST.
By default your ECONO button does nothing while on DEFROST. (AutoStop disabled)

You can change these defaults.
I've personally successfully changed the ECONO button default so the car will go into AutoStop while in DEFROST mode, but didn't have success with controlling the AC.
Here are some instructions, thanks to BUZZ70 (Mark):

The procedure to enable the ability to turn off the A/C when in defrost mode is:
1) Turn the vent control (top knob) to "face" (one to the right of
auto)
2) Turn the temperature knob all the way to cold (left)
3) Turn the fan control to "auto"
4) Hold the A/C and recirculate buttons down.
5) Insert the key into the ignition, turn to "Start" (or II)
6) Hold the buttons down for 7 seconds. The A/C light will blink,
then stop.
7) Release buttons.

To switch back to default, repeat the procedure above.

To allow "Econ" to be used, the procedure above is exactly the same, but you hold all 3 buttons in for step 4 until the Econ blinks.

I've heard the portion of this hack that disables the AC compressor while in Defrost mode applies only to the 2003 HCH model.

The best "hack" I've found for Defrost without compressor is to leave the fan set to OFF, and the direction control to DEFROST, which helps to keep the windows clear.

If they do fog up I rotate the fan control to HIGH for 10-30 seconds until after they have cleared again, then return the fan back to OFF.
I try to arrange this while going downhill.