I live in Central Florida, where it is warm and humid! The temperature most mornings when I go out to take my dog for her walk is usually in the mid seventies with humidity around 55-65%. I have a 2005 S80 and have tried many sttings to get rid of this fogging, usually putting the air-flow on Auto, the defroster on, and the blower control on high. To make any noticable difference I have to put the temperature controls on around 75-76 degrees!! I have to use the wipers on intermittant during this time. It then takes about two miles at these setting before the windshield clears. If I lower the temperture setting to what I consider normal - around 65 degrees - I still have a fogged up windshield when I arrive at my destination, around five miles from my home!
This is not what I expected from a Volvo (even an old one), has any Volvo owner in Florida got any method that will solve this problem?
This particularly ticks me off as my previous vehicle was a Subaru Outback which had a heater strip across the base of the windshield - that ensured that the windshiled was clear by the time I got to the end of our street!

Note - this is not the first Volvo I have owned - but it is silly problems and omissions like this that may make this the last Volvo I will buy.

 

Open your windows.

 

Might be a leaky heater core, or check your AC level. The AC goes on with the defrost to evaporate any moisture in the cabin.

 

I don't think it has anything to do with Volvo or an S80 in general, but rather a fault with your specific vehicle. As someone has mentioned, issues with your heater core, A/C unit, etc. Something is not functioning as it should and your car needs service.