I ran into an odd problem with my 2002 Buick Century.
Driving on the interstate. Temperature in the teens. I'm not sure if it was road-splash, or a fine rain/sleet, But I couldn't keep the windshield from icing up. Plenty of heat. The heater/defrost slot felt like it was connected to hell.
Using the washers would clear it up, but then the windshield would ice up again. I was reduced to peering through a small "hole" near the botttom.
I've never run into this problem with a warmed-up car. The defroster was certainly putting out enough heat.... The only other variable is the highway dept is using some sort of new liquid on the roads instead of salt......
????