If the temperature slider is set to red (hot air coming out of the vent), turning AC on doesn't do anything to the air right?

Reason I ask is, many people I talked to believe either using cold air with AC on, or using hot air with AC on is "the" way to defrog the inside of windshield.

I believe using hot air with AC off is the best way. I know as a fact that using cold air with AC on makes frogging worse. Not sure if having AC turned on while using hot air helps any. I thought when the slider is set to hot, whatever cold air being produced doesn't even go into the circulation. Is that correct?

 

you can have it on warm or hot
the ac helps remove the condensation from the glass

 

I have, in the past when I used heat, run my A/C. It's like having a Heat Pump system. And it helps in the long run, so I have been told, with the A/C being run.

Hey, I'm no pro at A/C. Who here is? They should post.

 

Adding the A/C dehumidifies the air. It doesn't make it hotter or colder with the heat set all the way up. Running the defogger without A/C may or may not help - it depends how wet the air is. I don't like doing it because it drags down the efficiency of the car somewhat, but my girlfriend does.

Make sure to run outside air most of the time - it will actually keep things less foggy than recirculated air, even when it's raining out.