Audi A3 Saloon - Misting front window - peterb

Not so long ago we changed our 3 Series (our third) to a Petrol A3 Saloon (2016). We are utterly thrilled with the change except.... in cold weather. The front windsceen tends to mist up on the inside about 1-2 minutes after pulling away. The first time it happened was really quite dangerous as it was unexpected and we were on a main road.

Our regime is as follows.

1. Scape ice off the windows (using a spray if it's bad)

2. Switch on engine

3. Aircon is ON and recirculate is OFF. HRW activated

4. Having the aircon diverted full to the front window helps a little but only up to a point.

Any ideas?

Audi A3 Saloon - Misting front window - RT

Check the cabin filter and the AC condensate drain.

Audi A3 Saloon - Misting front window - badbusdriver

I would agree with RT. The only other thing I could think of would be is a damp carpet, but I'd expect the condensation to be constant if that were the case, not just after you start it up.

Audi A3 Saloon - Misting front window - concrete

If it is the same body design as the larger models, A4, VW Passat, Skoda Superb etc then this problem was cured when I drained the panel at the back of the engine bay just below the windscreen. Plastic cover off to reveal the battery then at the bottom of the panel there are drain holes which were blocked. A couple of inches of water in the panel. Drained this and no more damp carpet or misting front screen. Maybe the same for yours. Good luck.

Cheers Concrete

Audi A3 Saloon - Misting front window - daveyjp
The aircon probably won’t operate when it is really cold so it is ineffective. On very cold days I turn all the heating off, this keeps the water in the engine block circuit so it warms quicker. After 5 minutes the water is warm enough to heat air to the windscreen.
Audi A3 Saloon - Misting front window - RT

Most modern cars use air-blending heaters, so the coolant is circulating in the heater anyway.

My VW Touareg has a myriad of valves in the heating/cooling circuit - three thermostats in the engine, one for the block and one each for the two heads - one for the transmission heater/cooler - and one for the cabin when the parking heater is used, so only the cabin is warmed, not the engine - of course if I'd ticked the 4-zone option it woukld have had even more valves

Audi A3 Saloon - Misting front window - bazza

It could well be the notorious VAG failing of rain water leaks into the cabin but usually see that when the sun heats the cabin up and then the water vapour condenses out on the screen when the outside temp drops. But I've also encountered this on the Octavias when using the a/c. On startup, the residual damp air somewhere in the ducts blasts on the cold windscreen and mists up in the first minute. I found that turning the a/c off and running with heater on full for a minute or two before switching off does solve that. Also, as above, turning all off and closing the vents will help.

1st world problem though, really! :-)

Audi A3 Saloon - Misting front window - Engineer Andy

It could be that any moisture in the car (including and especially from occupants breathing out) builds up quickly because the route that air is expelled from the car (to be honest, I'm unsure where from - perhaps via the back seats and the boot?) is blocked somehow to some degree, and will only be made worse if the air recirculator is on.

I wouldn't be surprised if water ingress into the car (or blocked drain holes in the doors, or in the air intakes by the windscreen wipers [leaves etc]) also contributes by effectively reducing (even when the air recirculator is off or car is sitting idle) fresh, drier air coming into the car and reducing the relative humidity. This will be all the more evident in colder weather, when the dew point is lower and condensation forms far more easily.

Audi A3 Saloon - Misting front window - catsdad
My 2004 diesel Accord did this from new on cold damp mornings as did a colleagues. It was very disconcerting to set off with clear windows then about 2-3 minutes later the sceeen would mist right up.

We never did resolve it and assumed it was some valve or similar gizmo operating when the engine reached a certain temp which upset the air flow into the cabin.

We just got used to it, kept the inside of the screen clean and a good cloth to hand. It seemed to only happen when it was cold and damp weather. There was no apparent other source of damp and these were, as I say, new cars so damp pollen filters or other deterioration was probably not the cause.
Audi A3 Saloon - Misting front window - Engineer Andy

A damp filter could indeed be a contributory factor in the OP's case, if it hasn't been changed out on schedule. The water causing the moisture has to come in somehow, and stay within the ventilation system, likely at a low point where it can pool. A small gap in some ductwork may be the entry point. Several possible causes as I and others have said earlier, and may be a pain to find, though perhaps not so much to fix if all it requires is changing a filter, cleaning intakes or sealing up a hole of two in air ducts.

As well as the windows misting up, excess moisture in that system can also cause/exaccerbate significant bacteria build up, which will not be good for the respiratory health of any person in the car.

When the fault or faults causing the original problem are discovered, I would strongly recommend the ventilation system be disinfected/deodourised, at least by 'burning off' any residual bateria on the inside of the air ducts by running the system on maximum heat and full fan speed for 10-15 minutes once warmed up.

Often such procedures (including best practice in using the A/C system to keep it in good condition) are given in the car's manual.

Audi A3 Saloon - Misting front window - Dogfuzz

Totally agree. Never turn on AirCon till engine fully warmed. Indeed--if you have the patience-be a bit of a sensible anorak and stay immobile till temperature guage starts rising.. Another obvious tip-keep the interior of the windscreen clean at all times.

Audi A3 Saloon - Misting front window - Bromptonaut

Had similar on all my cars in cold weather going back long before aircon. Problem is moisture from occupants breath condensing on cold glass. Typically occurs more on driver's side if no passenger. For good scientific reasons I cannot now remember chemical de-icer makes it worse.

Solution is to use warm (not hot) water to de-ice. The warmth raises the internal temperature of the glass above condensation point sufficiently for blower and or heater to keep it clear. When I commuted to London used to fill a thermos with warm water before leaving the ofice so as to de-ice/demist at station. On sunny winter day like today thermal gain then rapid cooling at sundown would mean screen was misted before I'd left London!

If you've got water penetration by any of routes mentioned in other posts the 'cook/chill' effect above will have rivers of condensation on interior glass. As I found when my Xantia was shipping water via it's tailgate.

Edited by Bromptonaut on 09/12/2017 at 11:04

Audi A3 Saloon - Misting front window - Engineer Andy

Sometimes some professional de-misting window cleaners also help, probably to remove all the dirt, dust and grease (finger marks) which can attract moisture (essentially how clouds form), condensing on the panes as previously described.

I found the YouTube video from ChrisFix excellent on this, as he tested both the professional grade products alongside 'home remedies', some of which actually did quite a reasonable job. He also uses microfibre cloths to wipe off dirty/wet surfaces rather than a bog-standard sponge or chamois, which seem to remove more without smearing/leaving residue.

Worth the OP trying this as well as getting to the root cause of the issue and other tips given above. Its amazing how much moisture one person sitting in a car can introduce into its environment, and is especially significant in cold weather when the ambient humidity levels are significantly lower than in warmer weather, when the due (condensation) point is also a significantly higher temperature.

Audi A3 Saloon - Misting front window - SkodaIan

I've had a similar problem on my Octavia. What prevented it on that was selecting front windows de-mist even if it wasn't apparently needed, and opening the front side windows about an inch.

I think what happens is that the 'climatronic' is configured to heat the car from the footwell up, unless you tell it the windscreen needs de-mist.


Ask Honest John

Value my car