Not always, if the carpet and carpet padding is soaked, it will steam up while the heat is on just from moisture inside the car.
The one down fall these old Mopars had was they weren't vented very well and any moisture in the car would steam up the windows. All I drove back in the 80's was old Chargers, Dusters, Darts, Barracudas etc and everyone had a moisture problem when it rained, I always kept a clean towel near by to wipe the windows.