So ive noticed for a while now, my 05 TL is always leaking air through the vents. If I turn on the heat then shut it off, hot air continues to seep through at a slow, but noticable rate.
If I turn on the cooler air, then shut it off, cool air continues to seep through.
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It's always in a state of one or the other. At first I thought it was just the outside air blowing through slowly or heat from the engine as I'm driving but it is not. Any suggestions on what to check for to resolve this?

 

Only when moving? Does it do it while stopped?

If while stopped, I would guess the blower speed transistor is borked up and the blower never stops.

If only while moving, push the recirculate button which closes the fresh air intake. Otherwise, that is usually expected.

 

turn on the recirculate button and retest.