aTOMic

D'ya ever wonder if the (now retired) Audi engineers who debated these extra (yet important) complications ever read these fora, and occasionally send each other Emails... "Klaus, I toldt you das impeller would impede flow in the event ov failure, but Nooooooo, you zed "DAS IMPELLER IS NECESSARY""?!

In any case, I raise my glass to you guys, as you so scientifically go about diagnosing the problem; and to the incredible amount of knowledge present on AW.com.
I await the resolution!
-Tom

alh3010

I have similar problem on a W12. I heard the heater pump clogs up and restrics the flow though the matrixes. The pump impeller clogs up, this impeller is magnetically coupled /driven so no direct drive. I have souced second hand pump and valve unit and I am putting it into local garage today. I was thinking of doing it myself but on my 2004 UK A8L W12 you have to disconnect the compter cables and fibre optic cable to remove the electronis to get acess. So I thought I wouldn't risk any programming issues as the garage has all the equipment. I will let you know the outcome and I intend to dismantle the old unit so I may post some pics

MP4.2+6.0

I worked through this recently in several ways. A month ago I did a complete coolant change at the same time I did both my tranny and diff fluids and pulled all the coolers for those other fluids too. As in, I REALLY drained the cooling system. I also changed a small inline thermostat down by the tranny cooler (on a W12/S8) since I wasn't 100% sure of its integrity and it was fairly inexpensive.

I also used it as a chance to go ahead and pull the heater related valve block up in the plenum area under the ECU's. On the other post about the ECU's in this thread, moving those aside is not a very big deal either. Also for reference, I had changed the coolant back at 3 or four years of life too, and the dealer replaced the radiator right at then end of 4/50 warranty for some small seepage I spotted. So the coolant maintenance has been very good over the car's life. Have used G12++ OE and only distilled water since I first touched it.

I pulled the heater valve block fully out and disassembled every part of it that I could get to easily, being careful with all the o rings/seals and screws and such. Net, I found absolutely zero inside of it. Everything I opened was absolutely pristine and clean. Then about two weeks ago I had the car in to get a reflash to the latest TCU software (since I had already pretty fully changed the fluid and filter with a 3x drain regimen). I had them look at the A/C at the same time. They came back quickly and reported it only had about 300g of the expected 600+g fill spec for the refrigerant, so they charged it back to spec. It's CA spring here now so no super hot days, but it is in the mid 70F range, and hotter parked in sun already. Seems to cool immediately again, and without the somewhat sluggish and musty delay I had before. So I'm concluding that on mine it was a simple A/C charge and certainly not a fouled out heater valve block.

MP4.2+6.0

See my reply from today elsewhere in this same thread related to this and W12's.

alh3010

Had the heater pump and valve assembly changed but only worked when the garage hooked up their laptop. Looks like I have got a software issue maybe?
I have the MMI update disks and thought I would try running it in again but the CD changer isn't reading the disks tried a 2nd set of disks same drive error. Looks like I'll have to bite the bullet and put it into an audi shop! My keyless entry has stopped working as well. I will inform when I get sorted

parkrog

I am having a similar problem of no heat. Hooked up VagCom and confirmed the water valves are getting signal? Anyone know how to keep them valves open in VagCom; so I can confirm water flow issue? Going to blow out heater cores this weekend.

awdinut

even with the climate control set to "HI" !! Let me know what you find out after cleaning the cores. The fact that the air does not get any warmer even when I put it on recirculate makes me wonder if it might be a cores not getting water problem instead of a blend door problem. BUT, it seems unlikely that both cores would go bad at once. So that leaves me still scratching my head.

parkrog

Mine has same problem no heat. I flushed the heater core, no restriction, Flushed valve assemble and checked vagcom and its getting power. Confirmed power with vom meter. Finally took out valve assembly; took off heater core fittings so I could see seals, hooked up power, and sure enough valves not opening. Partially disassembled and found nothing wrong, perfectly clean. Shaft to seals is difficult to move up and down, has built in springs. Anyone taken shafts out? Suggestions. Re-installed and still no heat!
Anyone have diagram?

MP4.2+6.0

Describe more specifically what you did when you say "hooked up power" and "valves not opening." Did you power it from the solenoid connector(s) right there at the valve block? Did you power it externally? You say you tested with a meter. Did you find 12V supply, or something else?

There are no diagrams for this internally as far as I know, other than the basic block wiring diagram (simplistic) and the water hose connections. And you have checked water hose routing (or know it was never fooled with)?--if reversed you can get a no heat result.

Failing figuring anything else out, it sounds like a bad valve block. Big bucks part. Presumably you could bypass it right there at the block assembly with a couple of barbed connectors (like the 90 degree ones at the H/W store) and some clamps. If it flows heat, I think you probably have your answer. In doing this, I would unplug the auxiliary pump (the other plug on the unit buried underneath by itself, assuming it has one like a W12) and also interconnect those two water lines--there are warnings not to run that pump dry.

Bangerla

Did you apply 12V directly to the coils for the valves? If so, you have burned them up. I learned this the hard way on my D2, and ended up buying new coils.