96 Millenia ventilation system

Hi there, I need some help. YOu see, I have a 96 Mazda Millenia which runs good, even though it has 127k miles. Anyway, lately, I've been having a problem with the ventilation system not the AC, the system that allows you to "open" and lets the air from outside to the inside. If I run with the AC on, theres no problem, however, whenever I run with the AC off and the ventilation sytem open, I usually get hot air, which I mean, if the air outside is cool, inside the car the air goes in but hot. Does anyone know what the problem might be? Could it be the air filter? Thanks

When you open the outside vents to pull in air it will be hot. That air that it is pulling in is taken in right under the hood with the engine heat right there. It should not be boiling hot but fairly warm.