The 300E was sold only with the ACC in the US, no manual control models.
If the air only comes out the defrost and side vents, check the fuse -- default operation with no power is full heat on defrost with low speed or no blower. This happened on my brother's 300SDL in the winter, it wasn't until he was taking me somewhere and my feet got cold that we figured it out.
The fuse is probably corroded and loosing contact -- don't remember which one it is, but by now you need to check all of them.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!