Audi Repair: heat failure, heat failure, hot weather

Question
QUESTION: Jan my '97 Audi A4 has heat up to the firewall with the two 3/4" pipes. Both are hot. Are you saying that I should see the  valve inside the hose "move"? Also is this the same "heater pipe" you refer to? I understand the 2 small pipes at the firewall. Is there another pipe?

ANSWER: In one of the two pipes there should be a valve, this valve is normally operated by a vacuum actuator.  Make sure this works.  It may also be a good idea to flush the system through, depends on whether the cooling system has ever been drained/cleaned.  Let me knw what you find,  Jan

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QUESTION: Jan with heat in both hoses to the firewall, can we eliminate the heater core as the problem? In an answer you gave to Dick 1/2/08, you talk about a mechanism "operated by vacuum". You go on to say" if it does not move, then a little persuasion..." The question is, what type of movement should I see? This valve is inline with the hose. What movement should I observe? (assuming I have the right small plastic/nylon part)Wouldn't any "movement" be internal?

ANSWER: There is a little actuating lever which should move when the valve position is changed from open to closed.  Both hoses can be hot through convection so this does not mean that the water is actively flowing through the heater matrix...  There is also a heater control flap unde rthe dash, and this needs to let air flow through the heater matirx instead of bypassing it (summer or hot weather)  It could be that this flap is stuck.  Let me know what you find,  Jan

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QUESTION: Thanks Jan. I still don't see an actuator for the valve. Guess I'm looking in the wrong place. Can you direct me to a place where I can see a photo of the valve actuator to make sure? It might be the heater control flap since there seems to be no airflow entering the car unless the AC is on. When I lower the temp control cold air flows ok. What do you think?

Answer
The air flow will be OK, but one way it will go straight in from the outside, and one way it will go through the heater matrix.  The airflow direction is determined by a control flap.
 The heater valve is usually located in the pipes in front of the firewall; it has a vacuum line going to it, and a diaphragm actuator.  Let me know if you can find them.  The problem may also be discussed on the Audi forums, they might be able to post pictures; I cannot, sorry.  Jan