I have a 1996 A4 2.8L and my heater works fine, I have gotten the core flushed before, as well as an entire coolant system flush. When I turn on my "heater" from the climate control it blows out cold air. Wen I drive around town with the heater fan off, I can get hot air to flow out, but the second I turn on my fan to try to heat up my car, nothing but cold air. I was wondering if anyone else has the this problem besides me. It is a real hassle because the defroster dosen't work either. I had ice forming on the inside of my car on my drive home, while trying to defrost my car. If anyone has any thoughts or Ideas, let me know.
-Thanks

 

3 things, maybe 4.. Core is plugged, air in system, Air Mixer Servo (flap) stuck on 'Cold', or the Heater Control Valve bad..

The first 2 you know, but you should open the bleed screw going to the heater core again just in case.. The Air Mixer Servo is on the side of the fan box and is a DC motor. If bad, a code should be set in the Climate Control. The Heater Control Valve is a vacuum valve located in the line going into the heater core - should be before the bleed screw.. check the vac line going to it also.

 

as for the Air Mixer Servo, how could I test the DC motor, and how can you tell if it is bad.

 

Does your coolant temperature gauge go up 1/3-1/2 way while driving or only at idle? If it stays cool while driving, then stuck open thermostat.

 

something i would like to add about the heater control valve is that if your car overheats, the valve will automatically close, and will require you to turn off the engine and let cool and then start up for the control valve to re-open. As far as teh air mixer, you should be able to see/hear it. switch your climate temp from 60 to hi and you should be able to see or hear the flapper move. your ear needs to be by the blower motor area, obviously make sure the fan blower is on the lowest setting.....hope you fix it soon, its freaking cold out here

 

Not too sure about the A4, but on my A6 of the same year, the blower is under the plenum cover (between engine and windshield) right in the middle. The Mixer Servo is on the driverside right above the bleed screw in the black box. The lever arms you can see on the passenger side of the blower motor. All the way forward (towards engine) is hot. To rear is cold.