Originally Posted by dr.lee.baugh
Could be the blend doors are stuck.
Search the forum, there is much discussion about them
Only other thing I can thihk of is to make sure that the coolant line heading into the firewall gets notably warmer when you turn the heat on. Turn the A/C off, heat off, let it run to operating temperature and then stick your pinky on the hose, then turn the heat on. If that gets warm, there is a method to create a hole in the bottom of the glove box to help diagnose, should be pictures somewhere here or youtube.