I have a 98 Venture with about 165,000 miles. She has been well maintained and looks, runs, and drives great. While the heater and AC both work fine (front and rear), when I have the heater control **** set to the defrost/floor setting, I will hear a noticeable sound of some internal heater door closing shut and then begin slowly opening. After a minute or so, you will hear it shut again and the cycle starts all over again.


This seems to only happen when the heater control is set on defrost/floor setting. It also appears to be most noticeable when you are idling or slowing down. I do not hear any air leaks, nor do we notice any change in the heating efficiency or output. I do not hear any plastic gear stripping noises. I do not believe the noise happens on any other heater control setting.


My guess is that the noise might be the fresh air door, but isn't that electrically controlled?? I'm confused and annoyed by the noise. Is my problem vacuum or electrical - and which door?? And why just that setting?? Any ideas to solve this mystery???

 

I hear crickets... Anyone out there with any possible solutions?