[C5] air intake for hvac

[ClockworkC5]

recently when i turn the a/c on i can hear a noise coming from under dash passenger side. this weekend i wedged myself under the dash (fun) and removed the hvac fan. as i suspected some leaves had gotten pulled up into the fan. i removed them and replaced the fan. where does the hvac pull air from? has anyone put some sort of screen over this area to prevent debris from being pulled in? our cars are not equipped with filters to prevent damage to the fan. another strange note that i cannot figure out for the life of me. i removed the fan and it immediatly turned on full blast. luckily the squirrel cage (call it what you want) cleared the housing when the fan turned on about 75% power. i turned the car on and messed with the fan settings, but would not turn off. i had to disconnect the battery, reinstall the fan in the housing and reconnect the battery and everything works fine. ANY ideas????