2004 S80 Foggy Windshield issue?

[mmbbg17]

Hi, I have a 2004 Volvo S80. I live in a wooded area, and in the morning and at night when I drive my windshield fogs up quite quickly. The defroster will NOT make it go away. At first, leaving the wipers on would make it slowly disappear, but at this point that is no longer effective. As of now the only thing that helps a little bit is to leave the air on without the defrosters, but this is really a pain as it eats through my gas and makes me freeze. Any suggestions as to how to fix this? Thanks in advance!!

[jimmy57]

The air conditioner dehumidifies air and in certain temps and humidity levels it is what will keep the glass clear.
Humans make water vapor as we breath and also perspire. The glass is chilled by the outside air and is worse when there is dew on the windshield that the air will evaporate. The evaporation cools windshield even more. Now you have the most ripe conditions for the human moisture machine's vapors to condense on the inside of the glass. If you let the compressor run you get the benefits of it lowering humidity inside car via the condensing of water vapor on the evaporator to be drained out on the ground.
I think the miniscule expense for fuel is a far better solution than an accident from distraction of fussing with keeping windows cleared.

Volvo encourages leaving the a/c functioning year round. It will automatically be off when the temps are below around 40F and will function a very low percentage of time up to the upper 70's. The dehumidifying effects when humidity levels are higher has been shown to contribute to less drowsiness for the driver.
You can set temp control to a higher temp to lessen or eliminate any chill.

[chrism]

"...At first, leaving the wipers on would make it slowly disappear..."

Is the fog on the inside or outside of the glass?