Old climate control are notorious for developing bad connections in control units. I probably will try to get one for my B3 [for free or for symbolic price], because I'm familiar with soldering iron, so if I will get one that doesn't work properly, I will to fix it
Ppls who are familiar with audis but not with eletronics sometimes replace old climate controls in B3 and C3 with ones from B4 and C4, respectively.