I have an 85 z28 in which the previous owners redid the heater core. Unfortunately I have not been able to take the whole dash apart to see what's wrong, but the problem I'm having is as follows.

Vent selection does not change. Air continues to come out of the top front vents no matter which vent it is set on. Itt's a no AC system, but switching the vents to bi lvl, etc do not change anything. Switching to max does indeed seem to suck air from the inside (though I cannot tell if it is ceasing intake from the outside.)

My biggest complaint is that the desfroster also does not work. A slight amount of air comes out of the defrost vents even on full fan, but not nearly enough to defrost my window.

The oddest thing is that I can hear the door trying to switch when I move the vents.. I hear a "thunk" then a "click" when I switch to defrost. It's never in the amount of time I've had the car reliably worked. However the other evening I started my car just to warm her up as it was an extremely damp day (rained all week) and cold. I switched the vents around and miraculously they worked. Flawlessly. Heat ceased airflow from the top vents. Defrost blew out the defroster perfectly. However, this ceased to work after switching them around a bit and now I'm back to square one.

Heat works well, just does not come out the proper vents. As stated above, I hear the doors moving and trying to click into place. I do believe something may be getting stuck as sometimes the airflow out of each vent alters slightly when I change it.

I have tested vacuum a little while ago and it seemed to all be fine.

I'm unsure of the mechanics of it and the data on alldatadiy doesn't seem to give me too indepth a picture of how the vent system works.

Can anyone help guide me to figure out what's going wrong? As much as I don't want to do it, this is going to be my winter car as well and I cant very well drive without defrost working decently. I should point out that while I know tearing the dashboard apart will help me see the problem first hand... doing so is not going to be an easy option as I have no garage/driveway and park on the street. Not that big of a deal, but i know taking them apart can be a huge PITA and a day or more deal if a part is necessary.

Any help is appreciated.

Thanks!

 

Usualy when the air only comes from the defrost it is a vacuum issue since defroft is a default position. But you hear your doors work so there is some vacuum. Check the source. At the least it should come from the manifold to a T or a vacuum break. From there it should go to the plastic tube in the harness that goes into the car and the other part of the T goes to a vacuum resivour. You may have a leak and the doors will not work proper off of the engine vacuum so it needs the resivour. It should be located behind the fender near the left marker light.

 

Thanks Mike. Specially for the info regarding the defrost being default position.

 

No problemo