It sounds like the blend door is either stuck or bad. Its purpose is to open and close based on what temp you need. In one position, it will allow air to flow over the heater core warming the car. If you need AC, it switches again closing the door to the heater core.
Honestly, to access the door and actuator, much of the dash needs to be removed. Based on your description, I would say one of the actuators is bad. Here is a picture of one:
I don't know if you can make anything out from the picture, but I wanted you to get a view of what you are getting into. NOT A FUN JOB.
Let me know if you have other questions.
Tuesday, October 13th, 2009 AT 9:43 PM