heater box mod for VW cars with AC

A1 Volkswagens with AC had a design flaw in their heating system. the outer dash vents do not blow heated air. only center vents are heated. outer vents blow ambient (or cold air when AC is on). when you factor in poor insulation and any drafts or leaks associated w/ the door and glass, the part of your body towards the outside of the car can get cold whilst you crank up the heat and cook the half of your body towards the car's centerline.

There are two ducts that carry air from the heater box to the outer dash vents. While I had my dash out recently, i noticed the proximity of these two outlets to the front area of the heater box, which carries warm air. i figured i'd set out to seal up the ducts from the cold air that was their current source and create a new source of heated air.

There is nothing between the two oval-shaped outlets on the heater box, so i went to Home Depot's HVAC duct area and picked up a 3" diameter aluminum heater duct for $2 or 3. This is a rolled sheet that is not joined to form a tube, but rather has a seam that can be snapped closed.

I removed the two ducts and rolled the tube up and jammed it inside the two oval outlets (See the Green Outline in the Figure Above), so that if i reattached the ducts the two outer vents would be connected to each other but sealed up from entrance of any air at the heater box. after expanding the rolled aluminum, i screwed a couple of self-drilling, self-tapping #10 screws (maybe 1/2" long?) (See the Blue Dots in the Figure Above) thru the two oval outlets into the two overlapping portions of the rolled aluminum to hold it expanded against the inside of the outlets, sealing the ducts from the airbox.

The oval aluminum tube that now runs thru the htr box runs close to the heated portion of the heater box near the center vents. I used a dremel to cut a big "port" from the heated side into the oval aluminum tube. this allows heated air to enter the aluminum tube and thus the outer vents are supplied with heated air