Fresher from under the dash pad???
 

So in my 89 and a friends 86 I have noticed the same thing happens, which leads me to believe it is designed that way. Start with all of the fresh air/heat levers in the dash slid all the way to the left. Take the top Fresh Air/Heat slider on the dash and slide it to the right (opening the fresh air inlet) and air flows out into the floor area, which is normal. Then take the middle slider and slide it to the right, moving the air up to the defroster ducts just behind the windshield and you get fresh air from those vents instead of the floor, which again is normal.

However, in this configuration BOTH of our cars also get fresh air blowing out from under the dash pad, and not just from the area directly under the vents. Air actually comes out from the slot that is under the dash pad all the way across the car froth center vent to the passenger door. It is almost like the system is designed to do this. Anyone have any pearls of wisdom about this behavior that might save me ripping my dash apart to figure it out?

The plastic vent sleeve/cover behind (and under dashpad) has come loose inevitably allowing higher flowing air to blow out the gaps. You "may" be able to reach from the trunk, I stress "maybe", to do so you may need to move the air diverter/chamber?

You can check the connection on many of these tubes & plumbing from the trunk area before having to remove anything major

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