Ok ok, so I went off a little bit at the merest mention of the word "damp". Moist just sealed the deal. I'm in.
You could have a blown heater matrix. Its a little thing like a radiator that sits in a box with the fan or cabin air blower, usually inside the firewall, can sprout small (pin hole sized) leaks, leading to coolant loss. If you put your temp setting on hot and blower on full, you smell a slightly sweet smell of antifreeze (assuming your system has a good mix of 50/50). If you remove the pollen filter you might be able to see into the assembly (with a pussers right angle) if the mixer flap is open, and possible a small pool of green fluid (or orange if DEXCOOL- GM or VW) If you check your coolant tank you might be down a bit, they tend to leak quite slowly, as opposed to split hoses which will dump coolant a lot quicker.
In Saabs of a certain age this is known as the goldfish bowl owing to their predilection to let you drive round with a few pints of fluid sloshing around in it. As they usually involve removing some parts of the dash, its a weekend job. Let us know make/model/year and maybe someone can help with mechanics or diagnosis.
Anyway, your smeary residue (fnarr) seems to suggest it might be a coolant leak, and if you are trying to clear windows, you need to open the vent, re-circ will make it worse unless you have A/C. Some "climate control" systems run in re-circ if you select "MAX COOL" if it has a discrete button for that, or if you select 62F/16C on buttons or dials then it might go to "LOW" when it does the same (closes the mixer flap putting the car in re-circ and trapping you with the goldfish.)
To get shot of the smears on the inside of the windscreen, get a sheets of newspaper scrunch it up into a ball and give the screen a good wipe when it is practically dry, if that does not work, warm soapy water wash and dry off with scrunched up newspaper
Thanks i did see when googling a while ago the pollen filter could be the culprit so i checked that, it was slightly better afterwards so at least in part that helped!
Thanks ships_cat, probably a bit of a technical job for me haha but i will pass it on to some of my more mechanically minded chums to have a look at.
Sgtpepperband, no windows open- although once in a drive through car wash i left my sunroof open a bit by accident. Luckily i realised pretty sharpish by the fact i was getting wet/damp/moist (just for you ships_cat )