[willmax11]

Rather than trying to disconnect the A/C from running with the defroster
I decided on this low cost method.

Being a prototype it needs a little adjusting but works very well.
I used a hack saw to cut it but it was hard to match the curved section.
I attached it with 3 double sided tape from the dollar store.

I have tested it at -27C on the highway and it keeps the windshield frost free.
Even with no interior heater beforehand. You do have to set the fan on the front setting
until the heat builds up and then you can switch it to front/floor.

The secret is the fan speed at 3/4 and the volume of air passing over the
windshield, not the temp.
I did not have to use the defrost settings at any time.

Maybe Honda will change that 1/4"x 3" small window vent and direct the air flow onto the windshield.