Whats going on? I've a 1984 300D.
The heat works as normal for a few minutes after startup, then all vents close.
The only setting that gets air back through the vents is AC/Cold. However when rolling the dial back to hot the vents close again.
Shut off the car for a few minutes and restart - same thing though vents close quicker.
I've checked/resolder ACC circuit board with no effect.
Any Ideas?