i have a big problem with my front demister. it will not work the fan pushes out hot air to the side vents and the middle vents, only but not to the windscreen and its causing heavy fog inside the car. i have tried sliding the control, back and fourth only one time it worked for a while and then stoped. my car is a 92 corrado on a k reg please can anyone assist me resolve this probem thanks, in advance.