A4 heater, only blowing cool air

A4 heater, only blowing cool air

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flatsix3.6

Original Poster:

756 posts

180 months

Friday 7th February 2014
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I have a 2005 A4 Avant B7 and only blows cool/tepid air when on high setting, this started today.

Could it be an air lock as it's just had a new cylinder head a couple of weeks ago, if it is how do you get rid of an air lock ?.

Or could it be something else, your thoughts would be appreciated.

Rich_W

12,548 posts

211 months

Saturday 8th February 2014
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Could be but unlikely, check the coolant level, air locks tend to eventually end up in the tank. If the levels way down then possible. Or it could be a coolant leak


More likely though to be a flap motor not moving and closing off the cool air to allow the hot air into the cabin. 1/2 hour diagnostics at a place will tell them which one. Depends on which one as to how much the labour is to fit it and reset the basic settings.

flatsix3.6

Original Poster:

756 posts

180 months

Sunday 9th February 2014
quotequote all
Rich_W said:
Could be but unlikely, check the coolant level, air locks tend to eventually end up in the tank. If the levels way down then possible. Or it could be a coolant leak


More likely though to be a flap motor not moving and closing off the cool air to allow the hot air into the cabin. 1/2 hour diagnostics at a place will tell them which one. Depends on which one as to how much the labour is to fit it and reset the basic settings.
All the vents are blowing cool air, what would cause all the flap motors to fail, a fuse or could the heater matrix be blocked ?.

Edited by flatsix3.6 on Sunday 9th February 14:25

Rich_W

12,548 posts

211 months

Sunday 9th February 2014
quotequote all
flatsix3.6 said:
Rich_W said:
Could be but unlikely, check the coolant level, air locks tend to eventually end up in the tank. If the levels way down then possible. Or it could be a coolant leak


More likely though to be a flap motor not moving and closing off the cool air to allow the hot air into the cabin. 1/2 hour diagnostics at a place will tell them which one. Depends on which one as to how much the labour is to fit it and reset the basic settings.
All the vents are blowing cool air, what would cause all the flap motors to fail, a fuse or could the heater matrix be blocked ?.
BTW I've assumed the car isn't overheating and the temp gauge is ok when driving. That the hoses all get hot in the correct order and the thermostat opens as it should and the pump is circulating it ok. If you haven't already. Double check those things first smile More important in terms of preventing further issues.

Regarding the heater, there's 1 motor that does the whole system hot to cold. So if it's stuck in cold position, it won't matter where you direct the air. Vents, screen, feet it will come out cold. I would be amazed if the matrix was blocked very very rare. If the coolant is ok then the problem is with the hvac system.

btw They look like this


This is an A3 one but they are all similar.

kooky guy

582 posts

165 months

Monday 10th February 2014
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Rich_W said:
I would be amazed if the matrix was blocked very very rare. If the coolant is ok then the problem is with the hvac system.
Not rare at all. Very common in fact. The 'anti burst' nature of these matrices seems to cause them to clog very easily since the coolant flow can avoid the 'radiator' part of the matrix. Certainly on the B6, any form of air lock can also cause the heater to stop working and they can be a pain to bleed properly. The heater has a separate bleed point.

Are you getting any heat at all? If you're getting lukewarm air out of the screen vents then I would blame the matrix, although the sudden nature of the problem does make it sound a little unlikely.

Rich_W

12,548 posts

211 months

Monday 10th February 2014
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kooky guy said:
...Certainly on the B6...
But the OP has a B7. Hence what I wrote smile

kooky guy

582 posts

165 months

Wednesday 12th February 2014
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Rich_W said:
kooky guy said:
...Certainly on the B6...
But the OP has a B7. Hence what I wrote smile
Same heater.

Rich_W

12,548 posts

211 months

Thursday 13th February 2014
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OK. How many blocked matrixes have you seen first hand on Audi A4's? smile I'll be surprised if the OPs problem is that. But then he hasn't replied recently so who knows laugh

Guyzza75

2 posts

98 months

Wednesday 6th January 2016
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Hi there ..I had this problem on my a4 2.0 TDI..on mine there was an air lock in my matrix radiator..to cure this I run the car and got warm then find the 2 rubber hoses that go into the car for the matrix..mine are dead centre under bonnet at back to left of battery..anyway undo the clip and pull it back ..then if you look on the rubber hose there is a small like pin hole in it around an inch back on the rubber hose ...gently pull back the rubber hose until the pin hole is clear of the metal pipe and air will hiss out ( I left my engine running).. When the air stops coming out and water squirts through the pin hole your done.. Tighten up the clip again !.. Please do at your own risk and be careful ..1 ..the metal pipes from the matrix radiator are soft aluminium and damage easy when trying to remove rubber hose and are usually very tight 2.. Be careful of hot water ...this worked for me after changing thermostat and temp sensor and still cold blowers :-) p.s the top was the only one I undid and was the tlreturn to engine ..hope this helps everyone ...I have heard stories of head cracked ..water pump gone etc.... All along was an airlock stopping hot air circulating for heating ..

EAMF Ltd

1 posts

87 months

Thursday 8th December 2016
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Hi thanks for the info ref Audi A4heater blowing cold air only, I was told could be the water pump,but I had them follow your instructions first ref air block in the system and it worked,the Heater now works as it should much appreciated
Eddie

Tonsko

6,299 posts

214 months

Monday 12th December 2016
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Thread resurrection! Apologies.

Have B6, cold air blowing. Blows warm air when revved.

The matrix has been cleaned out, a lot of crap came out apparently, and my guy had the system blowing hot after that, until he engaged the aircon, then it went cold again. The pipes leading out the engine into the system can be red hot, but no heat internally.

Any other ideas? A US Audi/VW site has suggested coolant flush then compressed air, but not sure about that.

BlueRinse05

1 posts

87 months

Wednesday 14th December 2016
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Just sharing my own experience on this topic. Had the thermostat replaced on my 2005 1.9TDI (manual) a week ago, then 3 days ago, having driven 6+ hours, the aircon stopped blowing out hot air. Have tried pulling back hose to/from heat exchanger to allow air out today and lifting reservoir so it's above the pipe, did eventually get some coming out but a bit sporadic and no hot air yet yet, but will try a few more times over next few days as another thread suggested.

Other symptoms, it will blow out hot/warm air for a short while if fan has been off for a while which seems to suggest some heat is getting in to the exchanger, albeit slowly. The bottom of the 2 pipes to/from the heat exhanger/matrix is hot (feels full of hot water), but top pipe is cold/empty so again, seems like water flow to/from heat exchanger is the problem (rather than flap that control air flow over the heat exchanger/matrix).

Garage couldn't diagnose, best suggestions were i) the heat exchanger/matrix is blocked (but this has been a sudden onset, not slow build up as some threads suggest is common with blockage); or ii) the water pump is faulty (but the engine temperature never goes above 90c and the pump was only replaced 2 years ago).

Will see if it improves in next few days with regular bleeding and update post.

Can anyone advise if I need to have the engine running whilst bleeding or will it bleed okay without? Also, better to do it hot or cold? (Obviously being careful if hot!)

Thanks

  • Update: Finally managed to get the rubber pipes off the heating exchanger/matrix connections at top of engine bay and flushed the matrix which seems to have rectified the problem (not uber-hot air yet but suspect a bit more bleeding and will be there). The hardest part was getting the pipes off as they probably haven't been removed in 10yrs so had corroded on. The Sealey VS352 Hose removal tool was a godsend!
NB. Not as much crud came out in the flush as I was expecting but it seemed to make a difference.

Edited by BlueRinse05 on Sunday 1st January 11:44

Rich_W

12,548 posts

211 months

Wednesday 14th December 2016
quotequote all
Tonsko said:
Thread resurrection! Apologies.

Have B6, cold air blowing. Blows warm air when revved.

The matrix has been cleaned out, a lot of crap came out apparently, and my guy had the system blowing hot after that, until he engaged the aircon, then it went cold again. The pipes leading out the engine into the system can be red hot, but no heat internally.

Any other ideas? A US Audi/VW site has suggested coolant flush then compressed air, but not sure about that.
Sounds a lot like a Water pump or thermostat to me. Have these been checked?

Tonsko

6,299 posts

214 months

Thursday 15th December 2016
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Rich_W said:
Sounds a lot like a Water pump or thermostat to me. Have these been checked?
The engine isn't overheating, so the water pump should be ok, no? Will maybe focus on thermostat for the next attempt, thanks!

kooky guy

582 posts

165 months

Thursday 15th December 2016
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Tonsko said:
The engine isn't overheating, so the water pump should be ok, no? Will maybe focus on thermostat for the next attempt, thanks!
Don't the impellers tend to fracture and effectively spin freely on the spindle on these water pumps? This also happened to mine. It ran ok for a while (but with no water flow through the matrix) until it eventually overheated on the way to work one morning after going up a long steep hill. Was glad to see the back of that money pit.

Tonsko

6,299 posts

214 months

Monday 19th December 2016
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The matrix has been flushed, coolant seems to be moving ok.

Drive it a bit more now (it's the other half's car mostly) and if you have it on low power (i.e. one or two bars) then you get warmth. Any more blow and it starts cooling down - presume because there's not enough heat exchanging going on.

Does this suggest that the matrix is buggered? I'm told it's a , as the dash has to come out frown

kooky guy

582 posts

165 months

Thursday 22nd December 2016
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I replaced the matrix on my B6. It's fairly easily. The dash doesn't have to come out, although access was a bit tight in places.
Google it, there are plenty of walkthroughs out there - that's what I did.

Tonsko

6,299 posts

214 months

Thursday 22nd December 2016
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Is this a Haynes Manual 'a bit tight' or just merely awkward? biggrin

Brendan

1 posts

76 months

Friday 17th November 2017
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Hi all. Having same issue with my A4 B6 1.9tdi. Replaced thermostat,sensor and only this week I decided to check the pump. It was fine but when I was in there I fitted new genuine timing belt kit including pump. Car can idle from cold with no heat until you rev it up and down. The the heat will work as normal all day until I drive it hard and temp needle will start heading past 90' very quickly. I've also noticed that after a drive the coolant level will have went down in reservoir and if I open cap there's there's a sucking pressure and coolant returns to maximum level

Brian robinson

1 posts

62 months

Thursday 31st January 2019
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Audi a4 b7 model i changed water pump thermostat cleaned out heater matrix. Still no hot air only when i rev it. I bleeded ok from engine then heater matrix still no hot air any help plz