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I think all of us have 380SE models (mine is a 1985 - manufactured in October of 1984) and mine is the same way. No matter the setting, I get most heat in the defrost, but I still get quite a bit on the outside dash outlets. I just turned them completely downward and they are pretty sufficient at warming the legs/feet. Of course it does not get all that cold here in the winter (and it looks like everyone else here posting also lives in mild winter climates), but I am sure if I lived in the north or a colder climate, I would be more concerned, but its not enough of a problem for me to bother fixing it now. I could understand though wanting it to work perfectly on a otherwise mint car (which mine is not).
My A/C does not work, but I am assuming if it did... all air comes from there too?
Seems like this is one of the first things to fail on these cars. I think a recall is in order.
Another thing I have noticed- not sure if it is normal, but if I actually put the mode on defrost, the air comes out at full speed- not matter the fan speed I set it on. Any other mode setting and it lets me select the speed with the fan speed switches, or it lets the automatic work. The HVAC is the last of my concerns now anyway, what, with something busted on my power steering system. To the shop next week I suppose.....
268,300 mile and counting.....
Good luck!