Vents stuck open/closed '93 525 IT

Hey!
I think this might involve something I read about a "stepper" motor or something but here is the issue.
When I am driving down the highway, and I take air through the vents from outside, it should be cool-ish (fresh) air, but instead, it seems to be coming from the engine comp. as it is hot.
The only time I get cold air is with my AC!
Someone has told me that the vents are controlled electronicaly and I am thinking they are not working or blocked open/closed.
Any ideas...?
If so, is this something that can be done by owner or the shop.

Thanks guys.....

Bman