I have had the STS about 9 months now and having gone through summer/winter season, I think I may have blend door issues.
In the winter, the heat is working, but the car is still cold.
In the summer, the air is working, but the car is still hot.
I believe from the blend doors not closing completely and letting outside air into the cabin. Gets a little better on Recirculate, but still not blocking the outside air.
Where are the blend doors on a 98 STS? No codes.