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.

 

Nice work on the deflector. Here in CA in non-snow areas, we don't have such a severe problem as you guys in the Frozen North. But Honda should resolve this problem at least in the next production design.

There is another solution and it does not cost much. Most auto accessory vendors carry a supplemental defroster that plugs into the 12 volt outlet with a fairly long cord so that you can set the unit on your dash to blow hot air on the windshield. You should not have to go to such lengths to be able to see in cold weather, but until Honda corrects the problem, this is another solution.