1990 Ford F250 fogged / wet windshield

oily substance on the windshield? does any air come out of the vents? smell like antifreeze?

it doesn't seem oily, more like condensation. the fan works, air blows thru vents, but does not get hot. I'm leaning toward heater core problem and looking for info on how to check and/or replace core.

to check it you can disconnect the heater core hoses and pressurize it. will it hold the pressure or does it leak out?

If it is blowing a mist out of your vents then it is most likely your heater core. I am not sure on newer trucks, but I have both a 89 and 92 Ford truck and the heater core on both trucks is in the same spot. It is behind the glovebox, inside the dash. It is a pretty easy replacement. Took me about 15 min. And it was only about $30. Another thing you could check is to make sure that your radiator has plenty of water in it. The heater core uses the heated engine water to heat the air so if you are low in water your heater will not heat the air. Good luck

yes it is behind the glovebox, and it really does sound like a heater core issue to me.

up till 93 or 94 was when the heater core was behind the box, after that you get to dismantle the dash to get to it.

bring in the old heater core, some part stores give out the wrong ones that will fit but when you go to put the hoses on there is no way it will work.