HVAC stands for "heating, vacuum, air conditioning"
if the evaporator is on the passenger side on these cars, it's very possible you're low on refrigerant (R-134a). also as scotty said, could be a blend door actuator. seeing as how your car is roughly 10 years old and probably hasn't had any sort of maintenance on the a/c system, you're low. take it to a shop, they'll charge it, fill it with dye, and you can go back if it stops working and they'll find your leak.
if it's a blend door, you're looking at taking your dash apart. sounds like a great afternoon. mine's getting stuck on heat and blowing hot air on my feet all the time. i need to fix it before my foot fights back
