I have a problem. When set for heat, heat comes from the right and left vents but not from the big one in the center. Instead cold air comes out the center vent with no hint of heat. What's wrong? Heater core, valve, something else. I really have no knowledge of this sort of thing so I need help.

Refrence: '86 4000s

 

okey, thats wierd. if you close the central wents does it make other wents blow harder and hotter?

 

No, it doesn't come out any stronger from the sides. But the center vent doesn't close either. When I toggle the switch that would normally close the vent, the air just comes out weaker than if it was left in the open setting. The switch itself gives no resistance to being closed like the sides do. But I don't car about that as much as I would like to have my center heater fixed.

 

On a 4000 it might be a broken flap or the cable has popped. I vaguely remember having some sort of a similar problem with my 4000.

 

But it's not the flap that's the problem, it's the fact that no hot air comes out at all, even when the heater is on. The flap is the least of my worries.

 

but thats the point, if its broken or cable off it would stay in closed position.
or open, it would be stuck.

 

The heater is supposed to take some of the outside air and mix it with the inside air. This is done so that your windows don't fog. If the flap is not working then you might be taking in too much out side air and blocking/bypassing the heater core.

Also check the temperature control valve under the hood to make sure that it is opening and closing properly.

If the engine warms up normally and everything else works it is possible that the heater core is blocked and will have to be replaced.

 

I have an 87 4k, it had the same symptom as your car's heater. The heater core on my car was leaking, so I replaced it. The entire heater box had to come out. I discovered the air going to the center vents is routed in such a way that it bypasses the heater core. The Audi engineers never intended the center vents to be used for heat- I don't know why.

 

I second that Audifan...... Thats what happened to my 85 4K.

 

I have exactly the opposite problem. Here in Africa I do not use the heater much on my A4 but suddenly I am getting hot air from the side vents and cool (not cold) air only from the centre vent. I took my car to an air conditioner specialists and they gave it a service, cleaning and gas recharge. Same problem. Someone suggested it could be a faulty heat flap. Never heard of such a thing. Can anyone give me a suggestion on how to determine the problem. The airconditioner used to work very well.