I'm having a problem with a 1998 S70 heating system; with the heat turned up, hot air is only coming from the side vents. The center vents are blowing cold. There is lots of heat from the sides but nothing at all in the center in any setting(Heat, Defrost, etc.) I suspect either a vacuum leak or bad servo/valve. Anybody pint me in the right direction on where to start?
TIA