Pontiac Repair: Heater, pontiac grand prix, grand prix 4

Question
QUESTION: My AC works just fine and the blower is working also. The problem is when I turn it over to the heater it blows cool air. At time it will blow warm air but not enough to warm the car up. It work just fine last year. (I do make sure the AC button is off). Could it be a fuse or what????

ANSWER: need more vehicle info, ie: year and make, thanks.

---------- FOLLOW-UP ----------

QUESTION: 2006 Pontiac Grand Prix/ 4 dr/

Answer
possible blend door actuator issue, is the vehicle under warranty?  the actuator is located inside the dashboard attached to the heater case.  Not sure if you were thinking of doing the job yourself or just looking for an opinion.  I can provide detailed instructions if necessary, hope that helps, have a nice weekend and good luck.