In this case, check the heater radiator for coolant leakage, the condition of the cabin filter, the mobility of the recirculation damper, etc. It seems that everything has been inspected and put in order, but the windows still continue to fog up.
But there is another factor that even experienced drivers may not know about. We are talking about rear ventilation valves that allow air from the cabin to the outside, but not back thanks to the upper suspension of the curtains. Depending on the make of the car, they are located in the wheel arches, under the rear bumper or in the door pillars.
If the valve curtains do not open for some reason, then the air from the passenger compartment will not be removed, which will lead to an increase in humidity and inevitable fogging of the car windows.
The ventilation valves are simply but reliably designed. They cannot refuse on their own.Usually, out of ignorance, they are welded shut during repairs or when eliminating the consequences of an accident, walled up with material used for sound insulation, or even completely cut out.
These valves also serve to equalize the air pressure in the cabin and outside when opening and closing doors.
