A D2 HVAC Heating challenge
 

Evening All,

Over the years I always seem to have problems with heating, my D3 had a blocked Matrix and the D2 S8 works perfectly but is always hot out the left vent.

Anyway.

My 2003 2.8 QS D2 has little or no heating.

Not the end of the world I thought, some basics should be covered and I can get it working again.

Though I have to admit this one has currently stumped me.

Hence I thought I would ask the wisdom of the collective.

So to cover the basics for what I have done already:

1) No fault codes on VAGCOM

2) I have run through the basic settings 08 HVAC and all flaps seems to move/ work as expected

3) I have flushed the cooling system, put on a new expansion tank and topped up with pink to the correct level

4) Car drives as it should, does not lose coolant and keeps at 90c as expected

5) I have flushed the heater matrixes and while they were dirty they have been flushed clean with no blockages

6) Using a laser thermometer the pipes into both and out of both matrixes get to 40 to 50c so seem to be getting coolant/ heat as expected

7) There are no air locks or leaks and I have bled everything

8) If I have the fans on low there is a little heat can be felt on the middle and rear vents

9) If I turn everything up to high and the volume of air coming through seems to drown out any heat that is in the system

10) The HVAC works for cold no problems and I can move the air around the cabin as expected with the controls

So this one has been a bit of a challenge and I have spent a few weekends looking into this one to try and resolve it as winter is here.

I purchased 4D0959617A Water Pump valves as whilst they seemed to work I was going to replace it to make 100% sure. Though interestingly the car is fitted with something different, not sure if someone has been there before on trying to fix this,

I have some Water Pump Valves in there, but the ones fitted to the car do not have round motor part on the back with the Denso sticker. Most odd, so not sure if this is a genuine part they fitted for that year or someone has bolted something else in there to try and fix it.

http://forum.a8parts.co.uk/picture.p...pictureid=1113
http://forum.a8parts.co.uk/picture.p...pictureid=1114

So it may or may not be at fault but I have the wrong part anyway.

The only other strange item of note is on 08 HVAC measuring block 14 the LF Vent Temp G150 is always really high (30c to 40c) compared to the RF Vent Temp G151 which is about 10c.

I looked at the S8 blocks and both vent Temps were about 10c so I am not sure if this is a faulty temperature sensor that's causing the HVAC not to blow any heat?

So we have a strange one here, any thoughts would be appreciated.

My S8 has a similar problem with always blowing hot. I swapped the valve block and now it is fine on the left but still blows hot on the right :mad: I think these valve blocks are just getting to the age where they are worn out so even used ones aren't necessarily an option any more.

The one you have is an early version with the round motor. Its simple enough to swap the connector over or make an adapter. Its theoretically possible to swap the motors over, but if the screws are seized you could strip them and end up ruining the block.

The first thing I would try is the two sensors in the air box under the dash since they are cheap and easy to get to. If they have failed the hvac unit will be controlling the valve block accordingly. They didn't help at all in mine, but they're much easier to do than the whole block so worth a shot. 4D0820539 - about £20 iirc.

Thank you for that.

Spent a few hours today having a looking and running the measuring blocks on VAGCOM.

Managed to take the G150 sensor out, but my word is it difficult to get to. I suspect I just have big hands or should have taken more trim out apart from the transmission tunnel cover. Getting to it, turning it, pulling it out and getting the thing out was very frustrating!

Anyway, had another old sensor available and confirmed with VAGCOM that disconnected I got 0c and the sensor plugged in I got a reading.

The new sensor gave a little lower temp reading than the prior one but there really was not much in it.

But as VAGCOM was running I could see the temps on G150/ 151 were say 22c so if I upped the level on the HVAC beyond the reading on the colder sensor there was heat.

Interestingly enough if I turned the HVAC off for a couple of minutes with the car running then turned it on again I got a huge initial blast of heat from it so there is heat in the system ok.

So I suspect I have two problems here, the readings from G150/151 are a little high so I have ordered new parts. Also the two sensors are reading different temps, I firstly thought this was just a bad sensor but the more I think about it the two heater matrixes are not performing to the same level.

As in one is much hotter than the other which is throwing the system out and confusing and already overly complicated HVAC system.

Therefore two new sensors and another flush of the cooler matrix I hope will solve the problem.

Its one way to spend time on a Sunday!

Used another hour of the fast disappearing daylight to purge both the heater matrixes again.

Flushed them through clean using a little pressure and lots of water.

Now G150 & G151 reading very similar to each other as RH and LH matrixes now seem to be in a lot better state. Ran all the basic settings again on VAGCOM to ensure flaps were all happy and in place.

Temps on the thermometers seem to read about 4 to 5c above the requested temp on the HVAC unit which seems reasonable to me and much more balanced now.

http://forum.a8parts.co.uk/picture.p...pictureid=1115

I have some heat there now but need to take it on a long run to check everything is working as it should.

What happened to the good old days when there was just a tap under the dash to turn the heater on +++

Hi Nognar it looks like from your picture that the valve block on your car simply has the motor missing, it is a magnetic drive to the impeller it's a pain to get off i removed the ecu box. many owners just disconnect this and are happy with the results.But i love this feature if parked waiting for someone or get out of the and i may be getting back in. it stays on for about 10min keeping the inside toasty and windows clear. so i'd fix that myself but its your choice.
But i suspect 40c to 50c upto the matrix isn't hot enough i would expect the temps to be upto 90c as the heater gets water that's split circulated near to the exhaust valves for faster warm up. I'll try and check mine so you can check. Dave

Ah, the demon Auxiliary Coolant Pump. :tuttut:
Yes, I'm one of those owners who just disconnected the wiring and am happy.
Didn't realise it was a magnetic drive though; I might investigate it further with a view to reinstating.

In this case, if the circulation is already compromised, lack of that pump could well be more of a problem. It does run all the time, not just when using the "Rest" function.

I had a look at the water pump and valves and its not the easiest thing to get to.

Hence took the flush/ thermometer/ VAGCOM route.

I need to drive the car for a few days to see what the temps are like inside the cabin. I just want a little heat in the winter.

The good news is the heater matrixes are flushed, clean and now producing some heat and clearly warm coolant is getting to them from the valves even if I am only reading 40 to 50c off the pipes. I am also getting 40c to 50c now on VAGCOM for the G150 and G151 sensors which is good news.

I agree if the coolant is 90c then you would expect that temp to be flowing but the other pipes in the engine bay holding coolant were all around 50c also. I suspect the cheap eBay thermometer and the thermal properties of the pipe wall itself to be taking the temperate reading down.

The main reason I was taking the temps was to check cold vs hot running on the car if coolant was being sent to the matrixes and that I had a drop in temperature from in to out of them showing the heat was being used.

A little thought on this, prompted by observations sitting in my car for a while today with the engine idling after not having been started for over a week.
(I wasn't specifically there to check the fan, but given recent problems decided to take note of its behaviour)

The main thing I noticed (recalled really) is that in "Auto" the HVAC does almost nothing for quite a while.
It's a boring autumn day, maybe 14/15C outside (but no sun) and the system is set to 21C both sides.
So, it's checking temperatures all round, including the coolant reaching it and initially pretty much decides to do nothing, fan speed on 1 bar only.

If I play with temperatures, absolutely nothing happens if I set it higher, because (obviously) there's no heat source. Set much lower and it starts to blow cold and increase the fan speed.
All very logical. +++

And without a powered auxiliary coolant pump there's probably not much, if any, hot water getting to the HVAC unit. It's probably all being recirculated to warm the engine up faster.

Of course, after a few minutes when the temperature gauge started to move, it all sprang into life.

So, my conclusions (at last!). It seems to me that MOST of the symptoms described here are down to normal/intelligent HVAC behaviour, probably exacerbated by inaccurate/faulty temperature sensors (but which ones) and the lack of an ACP motor.
Though low flow through the heater matrix if it's partially blocked won't help of course.

Incidentally my valve unit looks the same as the one you have installed (picture repeated), not like the one purchased. I can't actually see any motor or where it is.
Maybe under the air intake?
http://forum.a8parts.co.uk/picture.p...pictureid=1114

Interesting and thank you for that.

I suspect the system is not too far away from normal but the poor heater matrix performance was not helping especially as one was colder than the other.

I just need to spend some time in the car to see how it behaves, I have been bombing around in the A2 so not had the time in the A8 today.

I do know now for a fact I do get heat from the system that’s the key tick in the box I wanted.

It was this comment that made me wonder what was going on.
What happens if you let it warm up properly in that way then turn the ignition off and try the "Rest" function?
e.g. can you hear the pump running? You may need to override the fan speed down to minimum to check that or even go under the bonnet to listen carefully.