New used AC not blowing air out the vents

[a4b6dk]

Hello, 

I'm in the process of rebuilding my A4 B6 from 1din to 2din. I just bought a used AC control unit. But it's not blowing any air out the vents. I put my old one back in again after to test it, and air comes out just fine. Besides that, the 2din i just bought - the light in the rear window heating button goes off again after releasing the finger from the button. Anything i can do to fix this? Or do i have to buy another AC unit? The used one i bought came from england and i live in Denmark. That shouldn't have an impact on it, right?

Thanks for any replies!