99.99% just a broken spring, 0.01% all above

there is a flap to control the air circulation, fresh air or inside air, it is hold open with a spring, so in default it is fresh air, an vacuum actuator will close it if you choice inside air. when the spring is broken, it will stay at close position, even you choice use fresh air, that is why you have foggy window. to confirm this, find a quiet place, shut all the window, shut off radio, and then change air setting from fresh air to inside air, or vice versa, such as inside floor to fresh floor, or fresh vent to inside vent, don't change between floor or vent. wait for 1-3 seconds, if you flap working, you will hear a faint noise, if you don't hear anything, then bingo, you find your problem.