Have you noticed any bits of foam blowing out of the vents? This is a common issue on older cars - especially those in the South, I'm told. The mixer flap in your car may have old foam that is deteriorated, leaving open holes that don't separate the hot from cold air - hence the "luke warm' feeling.
This happened to my car that was bought in FL - see this thread:
http://986forum.com/forums/performance-technical-chat/42802-interior-vent-debris-2.html