Defog Windshield without dehumidifying

The quick answer is NO. Warm humid air recirculating around will simply lead to refogging of the glass. Add to that the air you and your pup are exhaling into an enclosed space with cold glass all around you. It's a lot worse than a foggy bathroom mirror because the other sided of the glass is much colder. It's simple physics - same reason a cold beverage glass sweats.
Bottom line; you need to lower the humility of the air within the cabin to keep the glass from refogging.

YMMV

 

Cold air outside, warm air inside.
Are you using the defogger button so it blows A/C air on the windshield?

You can also use a rag to wipe the windshield off...

 

Does spitting on it first help with the effectiveness, like with a diving mask?

 

Has that changed over the generations? I'm pretty sure my Gen 5 doesn't automatically crank up the A/C on defrost, but I'll check the manual.
How about a mix of defrost and front vent? Is there a position for that?

 

There are a few anti-fog products in the market, but due to the high humility - you'll constantly be reapplying it.

 

It's not like you have it on recirc, right?

 

You actually need it set for recirculate to dehumidify the cabin and prevent other glass in the cabin from refogging. I'm surprised that a lot of people don't know that. While your windshield may be clear and your rear glass, only if you've got the defogger ON back there too. All your side glass will fog up, so your door mirrors would be useless. The good thing is that you won't see that T-bone coming at you. Or the cars in the lanes next to you.

FWIW; it's raining today where I'm at. HVAC in manual mode, lo fan speed temperature set for 68F; didn't have to defog anything nor did I have to turn-on any defogger.

 

Gee, I wonder how people lived without air conditioning in their cars.

 

I'm a bit bougie; I had a swamp cooler option in my 1950 Oldsmobile. The heater core in that would turn the interior into a sauna. Manual doors, no fancy solenoid controlled mixer doors. DMV made me install seat belts on a safety check - told me they were missing. I told them that wasn't an OEM option, when it was new....

 

Very simple, set temp to HI and select the front defrost button.

You will still get heat from your normal vents and the windshield vents will defrost the window.

You should not be using or seeing the
"A/C" button/light on.

When selecting the front defrost button, if you have the system using recirculation button on, it will switch to vent in air from outside.

 

Pressing the front defrost button will not light the A/C button if you don't have that turned on.

However, that's not the same as saying an OBD-II scanner showing AC Watts will show zero.

 

All our previous cars being Honda, I was a little surprised, to see no windshield-only option. Screen-grab from a 2017 Honda Fit:



Short of stuffing something in the footwell heating vents...

It's been a while since I've used front-defrost, but I seem to recall it does light the A/C button (if it's initially off). Still (as you intimate regarding ScanGauge's AC WATTS?), it definitely is using AC.

 

If your caught in a rain storm and your wet.
Set HVAC to recirculate, AC - ON, crank up the heat. This will dehumidify your cabin and dry you off relatively quickly. Added bonus, all your windows will remain fog free, because of the lower humidity inside. If you don't recirculate and draw in cold wet air, any glass that doesn't have a heater vent blowing directly on it, will fog up due to the temperature differential you've just created.

Hope this information helps...

 

A rainstorm or other extreme outside humidity event may present about the only example where recirc would be a better setting for defogging.

Any other time, it's fresh for the win, as that purges the car of the humidity you and your passengers produce.

In any case, the car's going to make that choice for you:

 

Of note, at least with our Canadian spec gen 3: if you set vent mode to heat/defog, and have AC off, the car will surreptitiously use AC, as evidenced by the increasingly cool/dry feeling air coming from vents, plus ScanGuage shows AC WATTS alternating between zero and modestly higher value. The AC button light is not lit.

 

I'm assuming; if you don't use that windshield defrost button and only the HVAC controls - it won't over-ride your re-circulation choice.
I pretty much only use that button to force the engine-on, after an oil change - rather than do the witch-doctor dance with the pedals and buttons.