Bangerla

The valves on the coolant block can get gummed up. This happened on my D2. Its a bit of a pain to get them cleaned out, but then they do work better. Just dont try to test the coils using 12v, you will fry them.

MP4.2+6.0

Given stuff I find in Audi cooling systems--or any for that matter--after a bunch of years some gumming up/deposits sound right. I have a bit of the opposite season issue actually. One side of my dash blows warmer than the other on start up to cool down interior in the hot months. I suspect that something like this in the heater circuit is hanging up some. Because it's on one side more than the other, I've focused more on this block too. I plan to drain and replace coolant shortly anyway, so I think this is the impetus to take that valve block out and give it an inspection and whatever clean up is practical. Big bucks part, so it's time for a DIY check/refurb. when I have the coolant system open/drained anyway.

awdinut

One thing is that the VOLUME of air coming out of the vents is greatly reduced. I always keep my fan speed at '5' because that is the highest speed that is still acceptable to me noise wise and '5'has always been adequate for heating or cooling. Now, '5' puts out so little air I can barely feel the air with my hand; it takes '10' to get the flow that I used to get from '5'.

Clue 2: When traveling at highway speed the temperature of the air from the outer two vents is quite cool (not as cold as the 20 degrees outside today) where as the center vents are a little bit warm with the temp control set to 'HI'. And at city street speeds the outer vents return to emitting barely warm air...but still not as warm as the center vents.

And no work has been done to the valve unit et al since I have owned the car. I replaced the coolant tank myself a couple weeks ago, but I had a tech check the system for air a couple days ago.

MP4.2+6.0

That would be an airflow issue, besides or on top of a water flow issue. The obvious is then to see if your HVAC filter is clogged. Have you changed it recently? Of course that is on the fresh air side. If you hit the recirc button, is there any difference? Or, maybe fan motor is dying? Or further afield theories like your heater cores are covered up on the OUTSIDES by dust and crap and the air can't flow over them, or you have backed up a bunch of (now cold) water w/ possible clogged drains (which would likely smell up the system too)?

Anyway, a variety of scenarios in here, including a few easies to check--recirc. button, filter age, etc. Also, have you run through the VAG COM self test routine given this new clue too? That would spin the fan up, open and close the recirc door (and others) and a variety of other things that could overlap diagnosing clue #1.

FWIW, Clue 2 is less certain or obvious to me than Clue 1, but the difference from city to more open road is maybe suggesting that auxiliary pump in the valve block function is doing what it can, but your basic motor circulation is poor or faulty. Have you ever changed the water pump, like w/ a timing belt service? (as in, possible failed impeller) Any overheating clues, especially before weather went cold? Others would have to chime in on D3 4.2 set up vis a vis thermostat, since I just know my general experience is the heater circuit runs before the thermostat even opens. But as I say that, it reminds me that maybe your thermostat is stuck in the open position? I also don't know/remember anymore if Audi thermostats fail in the open or closed position now; obviously open is the smarter design to keep from frying motor, but then would lead right to these kinds of issues when cold. That would mean no overheating, but slow to warm, would run too cold with open road type driving compared to in town in cold weather, etc. So, any thermostat change to date?

Boiling all this down to best early guesses: 1. Check HVAC filter, 2. Run the self test on HVAC via VAG COM if not done already, 3. Think critically and investigate (winter) symptoms of bad thermostat, if that is you think possibility of water pump impeller failure or shaft uncoupling are low. If you happen to need a timing belt change anyway about now, it might be a good time to do the larger flavor of the job w/ water pump and thermostat.

awdinut

First to adress your questions (and thanks for your continuing efforts on my behalf by the way !) I had the T-belt done 2 years ago and the bill shows a t-stat. Did an R&R of the cabin filter today...its 2 years old but is not clogged. And pushing Recirc does not help any of the issues. And I turned on the recirc when the filter was out to make sure the flaps were closing.

On to new business : went to a different tech today and he did the VAG COM OUTPUT test you suggested. The only fault produced was for part V199 'MOTOR FOR BLOCKING FLAP; DEFROST AND BODY VENTS'. I have no idea what that flap does so I dont know if it could be my problem.

I will add that I sat in the car as the various components were activated and at times the airflow was what it should be. Infact, after I left the system seemed to be properly warm and definitely had normal air volume for #5 fan speed I use (although it was 30 here which is much warmer than when this started and would therefore produce comensurately warmer air). But then I turned the pass temp setting to 'HI' and the airflow went back to nothing and has not been right since. Tech also suggested I do a capacitive discharge of the car's electrical system because sometimes odd things are solved by that...any thoughts there ?

MP4.2+6.0

On the V199, you would have to look that up via Bentley or maybe the 2004 intro HVAC SSP, but that sounds like the flap that would push the air up through the upper defrost vents as an alternative to the normal dash routing. Obviously if a lot of air is going up there, your regular airflow will seem weak. Have you tried the forced switching via the heater control panel for defrost only/dash only/ and footwell only to see what happens?

Still doesn't answer the weak heat output from before though. I would still keep the thermostat possibility on this list given the descriptions, plus maybe consider whether other things are exacerbating the cold symptoms--are radiator fans running when no need (which is also a pointer the AC system is activated as it will also be in defrost unless cold temps lock it out), have you switched of f the compressor for sure via the "Econ" setting in the menu, etc.? I also don't really know the pre-fishmouth front set up, but can you get some cardboard in front of the radiator/AC panel. A classic thing I try when I want to se what happens if I heat the cooling system up more by restricting airflow temporarily, especially in winter.

Electrical system stuff you asked about: fancy words you heard, but sounds like a batter load test to me. Yes, the car can get flaky on electrical stuff as battery gets weak, but I haven't heard that so much w/ HVAC. But if your battery is more than 3-4 years old, it's getting past its prime anyway or could go pretty suddenly, especially in winter. In that situation, it might be something just to spend the $ on and replace anyway. Cheap compared to a bunch more diagnostics and makes a battery breakdown much less likely in next several years minimum.

Bangerla

How did the tech check for air? Get the car up to temp, and open the bleed valves next to the valve block.

Mister Bally

By the way; any chance that the problem is the blower motor? The brushes do not last forever and mine behaved erratically as it reached the end of its' useful life. No air meant no heat. It is not too difficult to replace.

awdinut

he opened something in that vacinity.

awdinut

I can hear the fan change speed as I dial a different speed number. Also, when the VAG COM OUTPUT tests were being run I was in the car and the fan air volume etc, and everything else worked fine