First, it sounds like you have a vacuum leak. The vent doors are actuated by vacuum. When you accelerate, vacuum in the engine drops. If there is a leak, the air's direction usually changes. Check under the dash for vacuum leaks and under the hood.
Check out this guide
https://www.2carpros.com/articles/air-vents-stay-in-the-defrost-position
Now for the AC that blows heat. There is what is called a blend door. It is located near the heater core. In one position, it allows the air from the blower motor to go past the heater core. The other position allows air to produce cold air. If that door is stuck, you will always get heat. Make sure it is working and not stuck. Additionally, this could also be related to a vacuum leak.
Let me know what you find or if you have other questions.
Joe
Feb 2, 2010 at 4:13 PM
