98 Volvo S70 heating/air conditioning problems

My air conditioner works pretty well, but when I try and increase the temperature to put the heat on a)a foggy gas of some sort comes out of the vents and fills up my car, b)it has a funny smell, and c)all of my windows fog up, especially the windshield, and the windshield defroster does absolutely nothing at any temperature. The only time when it works is when it rains (because my windshield ALWAYS fogs up when it rains). Note: even when it is cold outside and the heat is not on at all, the windshield still fogs up. Help??

You’ll need to describe your funny smell a little better. Does it smell sort of sweet, like ANTIFREEZE FLUID? Or does it smell moldy?

I would say it leans toward the sweet side…not really moldy. A few other notes…the fog on the windshield won’t really wipe away and there is also a crack in the windshield just in case that has to do with anything.

You have a leaking heater core or hose connection inside the firewall. Is the passenger side carpet getting damp too?