Mystery Mist

[evilally]

For a while now I've noticed that my windscreen has a tendency to mist in one particular area:



Is this a sign that the heater matrix is leaking? The car doesn't seem to lose any perceivable amount of coolant. There isn't any odd smell but it does take the AC a while to shift it. Most annoying.

[spider]

Does it mist up overnight when its not being used ?

It could be a tiny amount of water vapour just somewhere that causes it, ie some drops in the footwell or suchlike.

If it mists up when you use the heater (no a/c) then that is a sure sign of the matrix.

[evilally]

The picture above was taken when the car was parked up for 2 hours, screen was clear when I parked. If I switch off the AC it usually comes back

[spider]

Any water leakage ? , spend a few minutes in the footwell with a torch looking up. It could be something silly like a screen seal just making the odd drop etc. Not enough to make a puddle in the floor just enough to cause it to mist.

I don't think the actual heater water piping itself fails often but while you are there have good look take trim off etc.

AC dries the air which is why it can go when you use that, same reason for using it in winter months as you know.

[evilally]

Thanks Andy, this evening I put to good use one of my Christmas presents, a borescope inspection camera:



....I wiggled it up between the lower trim and carpet, and I can see what I believe to be the lower part of the matrix housing. It looks wet, and has blue residue:




.....not a very clear picture but I've circled the blue residue.

I suppose I can be thankful that on a right hand drive 406 changing the matrix doesn't require the whole dash to come out and is reasonably straight forward from what I gather.

[addo]

You're supposed to install the "fogger" nozzles in your intake manifold, not the demister ducting.

[mark21td]

Could it be the A/C condencate drain being blocked, alowing water to sit inside the heater box.
does any water puddle on the floor under the car when the A/C has been on ?

[Bick]

my mates 406 also does this but it is much worse all the windows steam up - my first thought was heater matrix leak but no leak found and car does not lose coolant.

No wet carpets but the A/C drain blockage may be the next point of call.

[evilally]

Thanks guys, I'm reasonably confident that the leak is around the heater matrix given the result of scoping, but I'll check the AC drain while I'm there.

Bick, a common cause of all of the windows misting up is the recirculation flap motor failing. This results in the flap sticking shut, no fresh air getting into the cabin and a build up of moisture. Take the pollen filter out from under the scuttle panel and check that the flap is actuating when you press the recirc button. Another tell tale sign is a creaking noise from behind the glovebox, as the motor is running with stripped gears. They are very expensive so most folk just remove the motor and push the flap open.

[spider]

The sign as you know is the click click from behind the glovebox. In theory the dash comes out for it but everyone just used to snap a piece of plastic off to get at it to 'fix' once you'd pulled the glovebox out.

Shame they went from the lever/cable to the button recirc on / off as the early cable ones (only models without AC) never failed.

Recirc motors are reasonably common, I'd jam it open so its always fresh and unplug it or remove it personally.

[Bick]

Thanks guys i will have a look at the recirculation flap.

Have a happy new year

[evilally]

Ok, I'm having real trouble with this. I got the old one out, it involved removing the glovebox and a couple of other bits and pieces, and trimming away parts of the dash (they can't be seen once re-assembled). I have new O rings from the dealer. I'm struggling to get the alloy pipes to seal in the new matrix (and just for fun I tried the old matrix with the same result). The pipe connecting bracket is done up tight, and the pipes look to be engaged fine. As soon as I start the engine it starts to leak into the footwell I've fiddled with it for hours. I'm tempted to bodge it up with some gasket seal but I'd rather understand what I'm doing wrong here?

[spider]

New seal ?

Let me check parts (five min)

[spider]

Seals (item 3) are new yes ?

Slightly large pic but easier than trying to split it and if its small you cannot see enough detail.

[evilally]

Hi Andy, yes brand new OE seals.