sullyj

We're in the start of winter here on the East coast and I've noticed that it takes an unusually long period of time for the cabin of the car to now warm up. The temp gauge is working fine and I recently had a new thermostat and temperature sensor installed (a month ago). The temp gauge will register dead center after 10 minutes of driving, but the interior heat is still just lukewarm or nearly non-existent. After I've been driving on the highway for about 20 minutes the car will finally become comfortably, but obviously something is askew. I never had this issue other than this winter season. I use an private Audi certified mechanic and he tells me the D3 has a heater component near the cowl of the car which may have gone bad and it's pricey as the dickens. Once the car has warmed up sufficiently with the climate control on "auto" and set at 75 degrees, I've noticed that the cabin will slowly get too warm and I then have to lower the controls to about 70 or cut the heat off for a bit. I've never had to move the climate control from 75 in the winter (on auto) previously and I'm wondering if anyone else has experienced this issue? I really don't want to have to go to the "stealer" and pay $150.00 for a diagnostic test.

dvs_dave

Sounds like classic bad heater control valve. It's a complicated unit with a pump, solenoid valves and sensors all integrated into one unit. You can carefully remove and dismantle it and maybe fix it yourself. Or just replace it. Part no 4E0959617C. It's around $1,600 new, but loads available used for a fraction of that cost.

volvopentaman

Having similar problems with my 2008 W12.

Mine also takes a bit of time to heat up (more than yours I think), I noticed that in AUTO position i get NO HEAT from anywhere else than the windshield centre defrosters. Driver's side gave out around 25-30ºc and passenger 35-45ºc, so a noticeable difference.

Fiddling around with the temp made next to no difference, unless setting it to low, then i got cold air from both. Putting both sides into HI didn't do anything more than at my usual 20-22ºc.

Setting my air direction to the floor gave me heat in both sides, around 45ºc on both sides. Setting it to anything else gave less heat in the driver's side.

I'm quite sure the defroster flap motor for the driver's side is busted.

Have a friend's MB S203 2001 with excatly same problem, except NO heat whatsoever in driver's side.

Had a similar problem in my 2006 W12, except really inexistent heat on the passenger side, while like 40-45ºc on the driver's side.

Seems to be the defroster flap motors that get busted.

So do a similar checkup that I did, fiddle with the temp and test if that makes difference on either side. Test putting the heat to floor-only, then to dash vents only and then to windshield. Note temperature differences on the sides!

Suspected bad heater valve block on both my cars at first, but I had hot heater cores on both cars on both sides, just no heat on one side, so it was a no-brainer to see that the valve block for 1600€ wasn't the culprit

sullyj

Thanks for the response. I'm seeing used ones on eBay for a tenth of the price of the new part. My gut is telling me this is definitely the culprit.

sullyj

I notice a few used units online, but many have the part number ending in the letter "A" rather than "C". Any difference in the units?

dvs_dave

Revision 'C' is the most up to date part so is the one you want to go with.

MP4.2+6.0

Like volvopentaman I once focused on this part as a possible issue, but then looked elsewhere and found mine. It is definitely what ultimately controls heater hot water flow though if that proves to be issue. I never went to trouble of doing so (and extracting the W12 one is harder due to ECU location), but if in doubt and it's winter anyway, you could bypass it with some fittings and clamps and then see if heater function returns well. Just tie the relevant in and out hoses together --one set for each side. May be a 5th one is there too--at least of W12--but it's been years since I played w/ it. You can also pull the solenoid covers IIRC and check/feel for action there. Some old posts on that if you search.

If you replace, there are a fair number of variants around for these, so be sure to get the correct part #.

Kerim Nuriev

Hi guys i have a audi a8 2004 with 4 zone climate controle in winter i have hot air coming on the passenger side on the dricer side its cold and dlower on the pasenger side works fine but on the passengers side its very slow please give me an idea on what can be
Thanks

sullyj

I replaced the heater control valve with a used unit. Improved slightly (very slightly) and now told the temperature control unit needs on the console replacement. I have the heater controls on HI and the cabin still stays lukewarm. Obviously this issue is driving me crazy and I'm now more convinced than ever that car's engineering is unnecessarily overly complicated. My 2nd A8 and highly unlikely to repeat this behavior. Heating control systems aren't complicated systems but Audio sure found a way to complicate theirs.

MP4.2+6.0

What year? Did you bleed it well after changing valve? ...Early years are harder to bleed. Dubious the dash control head needs replacing if it functions correctly for all the buttons. A VCDS scan would confirm either way; otherwise just throwing parts at it.