Folks new to the board so pardon an faux pas's.
My 83 TD is having fagging up issues. The middash heat vents don't blow air and there is a ton of pressure coming from the floor vents when on defrost... The mechanic I use says there some hose below that is leaking and pressure needs to build for the system to blow hard out the side vents. I have driven for 30 40 minutes an noticed no improvement in the air pressure.
Any ideas?

 

There's a vacuum dashpot behind the mid vents that you probably need to replace and you may need to replace the one that controls airflow between the floor/windshield as well. The other choice is the vacuum switch that controls air flow to all the dashpots under the dash.

The parts are relatively inexpensive from the dealer, but unless you have really small hands, that midvent dashpot is obnoxious to change out. If you do it yourself, buy the retaining clips for it as well. Invariably, the easiest way to take the old one out is to just break off the stems and the clips will go flying back into the nether regions under your dash, never to be seen again. You need three clips.

 

thanks helpfull stuff