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Thread: Hot air system

  1. #1
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    Hot air system

    Hi folks, just wondering if anyone is familiar with the hot air system or has experienced the same problem as me.

    Here are the symptoms of the problem:
    • When I turn the hot air on after starting the car the first minute or so is full of fumes, which seem to me to be exhaust fumes.
    • It doesn't matter how long you drive the car before you turn the hot air on. It could 1min after starting up or 10mins.
    • When you turn the cold air on no fumes out.
    Has anyone experienced this problem?
    Is anyone familiar with the heating system? How is the air heated? Where could there potentially be a leak?
    Is there any diagrams of the heating system out there?

    Any help appreciated.

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    <tuffty/>'s Avatar
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    tbh it sounds like you have a leaking heater matrix and the smell you are getting is actually coolant... the heater system uses engine coolant to warm the air... open the cap of the expansion bottle and have a sniff... if thats the smell you get its the heater matrix... if thats the problem then sadly its not the best job in the world... Westy has done this and documented it in his thread....

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    Cheers Tuffy, I will take a search for that thread.

    Just wondering in general how the heating system works. Does it draw air in from outside at a different location than cold air? Or is there just one location that air from outside the car is taken into the system?

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    Found the thread here My god fixing the heater matrix is hard work! . Westy describes the smell as "horrible spicey/musty smell of coolant"...hmmm, mine smells more like exhaust fumes tbh. But I will take a smell of the expansion tank and see.

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    Quote Originally Posted by metricspaces View Post
    Cheers Tuffy, I will take a search for that thread.

    Just wondering in general how the heating system works. Does it draw air in from outside at a different location than cold air? Or is there just one location that air from outside the car is taken into the system?
    Same location, the air is directed through the heater matrix when you want hot air or by passes the heater matrix when you want cold air...

    <tuffty/>
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    Oh that heater matrix job was so much fun!

    The smell I had was that of warm old coolant whih is a very distinct smell and nothing like exhaust fumes. Going on your description though it does sound like you have a matrix leak. I'd guess the smell would vary depending on how old the coolant is.

    I bought an A3 Haynes manual to do this job and it was very helpful in the steps to remove the dash in the correct order. My other piece of advice is to buy a genuine VAG matrix. Thy are a lot more expensive then the car parts places but I had fitting issues with 2 seperate ones from different parts places before I fitted a genuine one.
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    Westy, when you turned the hot air on you got a smell. Did this smell go away after a minute or so, with clean non-smelling hot air coming out? Or did the smell stay there as long as you left the hot air on?

    Should I be noticing a loss of coolant if the fumes are from coolant? Or is the amount so small that you'd not notice?

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    You won notice any coolant loss unless it's major but you'd also be getting a wet passenger footwell too.

    The smell never went on mine but I got used to it after a few mins. It would make me feel sick on long journeys though.
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    Cheers Westy, apart from a wet passenger footwell, is there anyway to determine if the problem is with the heater matrix without pulling all the dash apart? Like can you inspect this from the engine bay? Or can you take a limited amount of the dash off to see if coolant is getting out?

    Taking a look at your photos from My god fixing the heater matrix is hard work! I'm guessing there is no easy way without pulling all of the dash off :-( ?

    I checked my passenger footwell and it is not wet. I got my coolant changed last week as part of timing belt service...and now I'm not getting the smell as frequently, or maybe my mind\nose is playing games on me.

    I can't recreate the problem as easily as before...before if I started the car in the morning, then turned the hot air on after a few minutes, the first initial burst of hot air would choke you, really strong smell...so strong I'd have to open the windows.

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    No way of checking I'm afraid as the matrix is sealed away in the fan system. All you get is the inlet and outlet pipe in the engine bay.

    I left mine for a few months till I just knew the problem/smell had to be the heater matrix. When I got to it there was only a small sign of leaking (pink coolant dried in the matrix fins) but it was making a lot of smell.
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    Had this on my old A4... I left it for months and it was actually making me ill... only really realised after I had replaced it how much an effect it was having... this is still assuming its the matrix...

    On my A4 the windscreen would steam up and the smell of warm coolant is quite distinctive (hence asking you to have a sniff of the expansion bottle)

    <tuffty/>
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    once im my old vr6 golf back about 5 years ago on a freezing cold morning me and a work friend were late for work and motoring along a duel carriage way at about 100 then bam, car instantly filled with steam and i had to wipe the side window so i could see the central reservation... pulled up under a bridge in the middle! a guy actually stopped cause he thought we'd caught fire... treat me for topping up with water in the winter!!!

    if your exhaust is leaking near the pipes maybe it could get in???
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    Quote Originally Posted by <tuffty/> View Post
    (hence asking you to have a sniff of the expansion bottle)

    <tuffty/>
    Ok, had a sniff (and managed to burn my nose in the process when the coolant erupted up, oops!).

    I think the smell from the hot air does smell like the coolant. Kind of a musty strong smell from it.

    Also, as you mentioned there is only one input for air into the car, that the cold and hot air both come in the same way...the only difference being that for hot air it is directed over the heater matrix. So it couldn't be fumes coming in from outside the car as the problem would be there with the cold air.

    Sounds like me needs a new heater matrix :-( ... on the plus side, thank god I have heated seats to use.

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    Quote Originally Posted by Westy View Post
    The smell never went on mine but I got used to it after a few mins. It would make me feel sick on long journeys though.
    Presume you only got the smell when you turned on the hot air right? If you were driving without the air on, or only the cold air on, you wouldn't get the smell?

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    Quote Originally Posted by metricspaces View Post
    Sounds like me needs a new heater matrix :-( ... on the plus side, thank god I have heated seats to use.
    Good job the summer is coming. I decided I had to change mine in October!
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  17. #16
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    Quote Originally Posted by metricspaces View Post
    Presume you only got the smell when you turned on the hot air right? If you were driving without the air on, or only the cold air on, you wouldn't get the smell?
    This is correct but it was the winter and I needed hot air
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