Peculiar HVAC issue - no air but blower works?!

Hello!

Have read all threads I could find, dissected the Audi workshop manual and run repeated VCDS-tests but still do not understand what the problem is. No fault codes.

Issue:
Dialing in a high temp (23 C) on the climate control unit (outside temp 5-10 C). In the beginning everything works fine. Hot air blows from all vents (auxiliary heater works, engine is cool). Vents can be closed and opened and affects air stream.
After 30 min of driving. The air stream from all vents diminish slowly and almost stops. Blower works (opening the filter housing results in a small tornado). Air is hot but only trickle out of the vents. Car gets cold inside.

What is wrong? I was suspecting the temperature flap but if it closes I would get cold air wouldn't I? If I lower the temperature on the climate control unit I get a good stream of cold air. It is almost as if the heat exchanger would be clogged but there is a good stream of hot air to begin with. There is no difference if I engage the recirculation (the recirculation flap engages but it does not alter the inferior air stream)

anyone with experience?
 
I have a similar HVAC problem. Seems the heat flap misbehaves if I switch recirc on for a few minutes, then off again. If I do this, I get full heat, with no control. If I turn HVAC off, it goes off. If I park up and leave it alone for a few hours, it returns to normal. VCDS shows:
"01809 - Actuating Motor for Temperature Flap; Blocked or No Voltage"
Once normality has returned, I can clear the error.
I've registered my copy of VCDS Lite, and will try HVAC Controller Output Tests. Otherwise, it's glove box out I think.
My question is,
"is there an explanation or diagram, that shows air flow and the function of each flap?"
This would help me, and sunebralla.
Mac.
 
Thank you for the pdf Spike! I have a lower quality copy of the same document but the one you got is much easier to read. Still don't understand how come there is no air out of the vents. I also have to correct myself. When the air stream decreases it does so also when climate control is set to LO. No cold air flow either. At least not today :/

What is obstruction my HVAC air flow after 30 minutes of driving? Can't figure it out. Has to be some flap issue but how?

Next step is to harvest HVAC sensors, servos and control unit from a donor car at a breakers nearby. Swap them out one by one and see what happens.
 
What happens when you put the blower on Manual (+/-) rather than AUTO? If it changes, it's the A/C that's the problem.

RAB
 
Thanks for both links, I had started translating the German one, with Google Translate, but the English version saves that.
At least I have a clue from the VCDS code, but sunebralla does not. I'm thinking that if there are no fault codes, the HVAC Controller thinks everything is OK. So, maybe the electro mechanical part of the HVAC system is just doing what it's told, and the fault is in the HVAC Controller? I'd suggest swapping that first (probably the easiest to do as well) before getting into the actual mechanics of the HVAC system.
As always, good luck. Mac.
 
Looking at the air flow diagram, could it be that the evaporator is iceing up (after 30 mins), and blocking the air flow? It's straight after the pollen filter, hence the tornado from there. Have you tried with the ECON button on (AC Off)? If so, maybe the AC is "stuck" On permanently, due to a switch fault? Mac.

Edit: If Evap is iceing, AC is on LO. Sensor or HVAC Controller maybe faulty.
 
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It may help to log the temp sensors as they must play a major role in controlling the flap positions.
VCDS may not record a fault code if the sensor is working even though it could be reading 20 deg out

Cheers Spike
 
Looking at the air flow diagram, could it be that the evaporator is iceing up (after 30 mins), and blocking the air flow? It's straight after the pollen filter, hence the tornado from there. Have you tried with the ECON button on (AC Off)? If so, maybe the AC is "stuck" On permanently, due to a switch fault? Mac.

Edit: If Evap is iceing, AC is on LO. Sensor or HVAC Controller maybe faulty.

If the evaporator is icing up, the ambient temperature is too low, in which case the A/C should be off.

RAB
 
If the evaporator is icing up, the ambient temperature is too low, in which case the A/C should be off.

RAB
Not if the controller, or the info it's getting (ie sensors) is faulty. It may well think the ambient temp is too high, hence it is trying to lower it. Mac.
 
Not if the controller, or the info it's getting (ie sensors) is faulty. It may well think the ambient temp is too high, hence it is trying to lower it. Mac.

Exactly. I did say "should".

RAB
 
sunebralla says:

"Dialing in a high temp (23 C) on the climate control unit (outside temp 5-10 C). In the beginning everything works fine ..... After 30 min of driving. The air stream from all vents diminish slowly and almost stops ..."

Even if AC is switched On (ie ECON Off) it shouldn't be working very hard (outside temp 5-10 C).
If AC is switched Off (ie ECON On) it shouldn't be working. Either way, iceing is very unlikely.
If it is iceing (we'll have to wait and see) then AC is stuck on LO. Don't have circuit details, but stuck relay perhaps? Fuse 38 check will either confirm iceing, or prove that theory and practice are not always the same!

PS: Does auxiliary heater refer to the Webasto? If so, could that be influencing/misleading the AC? Does/should it turn Off automatically?

Mac.
 
Thank you for all the suggestions! I have tried manual control. Good idea about ice in the evaporator! But the air coming out is really hot so i doubt it. Maybe i could stick an inspection cam in there through the air filter opening and have a look.

I will also take a drive with measuring blocks on vcds during the weekend. To see what the flaps are doing and sensors report when the problem is present.

.s
 
Thank you for all the suggestions! I have tried manual control. Good idea about ice in the evaporator! But the air coming out is really hot so i doubt it. Maybe i could stick an inspection cam in there through the air filter opening and have a look.

I will also take a drive with measuring blocks on vcds during the weekend. To see what the flaps are doing and sensors report when the problem is present.

.s
Do try it with AC fuse (38) out. That would rule iceing out, if the problem persists. Mac
 
Do try it with AC fuse (38) out. That would rule iceing out, if the problem persists. Mac
If you pull the A/C fuse, won't that also disable the blower, since it is controlled by the A/C controller? ECON should disable the A/C (and the electric heater), without disabling the blower.

Is this a problem with the heater matrix or even the water pump? The heat when you switch on would be from the electric heater but that would switch off once the engine warms up. If there is no or poor water circulation, there will be little or no heat from the heater. As for the blower, with ECON switched on with AUTO, the fan would run slowly until there is heat to distribute.

RAB
 
If you pull the A/C fuse, won't that also disable the blower, since it is controlled by the A/C controller? ECON should disable the A/C (and the electric heater), without disabling the blower.

Is this a problem with the heater matrix or even the water pump? The heat when you switch on would be from the electric heater but that would switch off once the engine warms up. If there is no or poor water circulation, there will be little or no heat from the heater. As for the blower, with ECON switched on with AUTO, the fan would run slowly until there is heat to distribute.

RAB
I think the blower is Fuse 16. Fuse 38 is AC. (+ phone + parking sensors). Fuse 38 will disable the compressor clutch etc, so no cooling.
PS: The symptom is No Air flow, so it's a blockage of some sort in the air flow path. There is air flow through the pollen filter at all times, and the evaporator is the next in the flow path, after the pollen filter. So that makes the evaporator the next suspect, to be ruled in or out. I think Fuse 38 will do that. Mac
Mac.
 
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Further reading of the description tells me that there is no clutch on the AC compressor.
The AC runs (belt driven), even when AC is Off, (at >2%).
The AC is controlled by means of regulating valve N280, which is continuously variable via PWM (Pulse Width Modulation), so, not just open or closed. The HVAC (Climatronic) Controller controls the N280 valve. So, if it fails open, AC is on, and uncontrolled. It seems to be screwed into the compressor itself, and has an external connector.

Mac.
 
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