My 83 Ranger has slowly developed a problem with defrost where it fogs the window. It has now become a major issue, as there are no settings (Defrost or Heat, Heat, Hi-Low, Vent, etc.) or combination of settings where window doesn't start fogging immediately. In less than five minutes all interior windows are completely fogged. This happens more quickly at night when the outside air is colder.
The vehicle is kept in a garage. Mechanic suggested water in heat box when I telephoned with question. Does anyone have any suggestions as to whatmight be happening here?
Thanks.
Anne

Possibly a bad heater core. Can you smell anti-freeze at all?

Yes heater core could be leaking.

Also if you have a/c , I believe you have a lever on your heater controls to choose between outside air and recirculate , make sure it is set on outside air or your windows will fog.

Possibly a bad heater core. Can you smell anti-freeze at all?

No anti-freeze smell. Have checked all hoses, connections, looked for signs of water leaks, and find nothing. I am ready to guess that it is heater core, too, which is definitely beyond my range of fix-it knowledge.

I took the truck out for a test drive in heavy rain yesterday and turned back after a short trip as all windows fogged immediately when testing. I seem to be getting wet air when I should be getting hot dry air with levers set on Defrost and Heat. Plenty of air comes through the vents, just the wrong kind.

Thanks for responding.

Anne

Yes heater core could be leaking.

Also if you have a/c , I believe you have a lever on your heater controls to choose between outside air and recirculate , make sure it is set on outside air or your windows will fog.

No AC. What you say here gives me another clue for my on-going diagnosis as it suggests that the outside air source is blocked.

Thank you for taking the time to respond.

Anne