05 f150 xlt supercab 303k miles. I have noticeable air coming through the vents when in the off position. A/c and heat work normally otherwise . Anyone else have this issue?

 

At 303k miles, that’s honestly impressive, but what you’re describing is pretty common on the 2004–2008 F-150s. When you feel air coming through the vents with the system “off,” it’s usually just outside air being forced through the HVAC box while you’re driving. The blend door and mode doors don’t fully seal airtight, and over time the foam seals around them deteriorate, which lets ram air push through the vents even when the fan isn’t running. If switching the selector to MAX A/C reduces the airflow, that confirms it’s just outside air routing. It’s generally not a serious problem unless it’s excessive or noisy. Fixing it would involve dash disassembly to reseal or replace blend/mode doors, which most people don’t bother doing unless they’re already in there for actuator repairs. On a truck with 300k+ miles, I’d call that more of a quirk than a failure.