If the film is accompanied by a strong, sour smell, you could have a small leak in the heater core. However, I agree that you need fresh air coming in to take the humidity out. The recirc. setting. is for quick cooling or heating only. In the past I was in Saudi Arabia visiting an oil company; my driver had a rear drive Buick, Le Sabre I believe. It was one of the very few days it rained (first time that year) and th windshield fogged up. The driver kept wiping it until I reached over and put “defrost” on with full fan. The windshield cleared up instantly; the only time I was ever called a miracle worker.