More information would be helpful. I am assuming the car is fogging up with the defroster going. there are a number of things that can cause this. One is a heater core that is leaking. the coolant causes the windows to fog up and will have a slimy feel to them. if this is not the case then the defrost vents at the top of the dash may be clogged or the exchange box has a problem with switching levels. check and see if you have good air out put at the top of the dash. If you do then go back to the first part of this message.