Sounds like 1 of 2 things....1, the hedgehog resistor needs replacing or 2. The digital Climate control unit needs replacing (or the resistor inside it)...or both !! If you havent got a digital climate control unit then its more than likely to be the hedgehog. If you HAVE got the climate unit then you can just replace the resistor inside it,they are prone to causing this problem.You can buy them plus the instructions from ebay and are easy to do,ive done mine before.