I noticed today with my temp slider to heat that while driving air is being forced through either my defrosted duct or my heater ducts if I have the selector slid to off.

Is this normal? I probably never noticed it in the past as I had it on cold till recently and felt heat.

If its not normal what should I be looking at?

 

If you accelerate or pulling a hill, is that when it goes to defrost? And when you are cruising or idling it goes back to the heat ducts?

 

Mine isnt a blend door change problem, mine is cable operated. My problem is when I have the blend door set to Defrost with the heater fan in the off position when I drive air is being forced through the HVAC system and comes out of the Defroster vents.

I switch it to Heat and its the same thing it comes out of the heater ducts. I switch it to off it continues to come out of the heat duct while driving.

I am wondering if this is how a dealer Air truck is supposed to operate or if theres some seal that is bad that I can replace to resolve this.