Interior fogging up in wet weather

[Kedaha]

Started about 6 weeks ago, driving 250miles on the motorway in the rain and no matter what settings or how long I left it running: all interior windows started misting up quickly unless I had A/C on. Even after running A/C for two hours, as soon as I turned it off they started misting up quickly and thickly.

If it's raining or wet out, within 30 seconds of turning econ on, fresh air only on, and lowest selectable temperature every single window in the car is thickly fogged up - so thickly that water eventually starts running down the windscreen.

I've replaced the pollen filter(with a carbon filter too!), i've rodded the drainage hole in the plenum so that's clear too. I don't think there's a leak under the carpets because the car doesn't mist up when not in use, there's no leak in the boot.

Any idea what the hell it could be? Is there a way for water to be getting in to the air ducts somewhere, which is leading to the air on econ being damp and throwing moisture at the windows?

[chipsceola]

Is the recirc button 'on' that would give same symptons and can be on as default.
Chips

[Singvogel]

I would expect my windows to mist up on humid/ wet days without the AC.

Having 'Recirc' on would make it worse of course.

Many people only use the AC in warm weather and treat it as Air Cooling only forgetting that is is an Air Conditioner.

I use the AC almost every day of the year to dry the air inside the cabin.

If this didn't happen before then you may of course have a leak from the heater matrix.

[scouseeric]

Hi Kev, if you've a sunroof then check the drain pipework hasn't come adrift, under the glovebox. hth

Eric

[Kedaha]

Eric: Will do when weather clears. I still don't understand how a leak under the carpets would result in the above symptoms though.

[Singvogel]

I would guess / suggest that if there is a leak and underneath the carpets are wet you will have pretty high humidity inside the car.

It will also be warmer inside than out.

The outside of the glass will be cold so you get condensation.

Good luck in solving this.

[Dashiel]

check the seals around the wind screen. have you had it replaced in the past? Use tissue paper to push into the cracks where the windscreen seal is to check for water - you can't see the water and you won't be able to feel it with your fingers.
i have had in the past water coming in past a failed seal on my old Mondeo - the water ran down the pillar, into the glove compartment and then to the floor. (I would never have known other than my electrics started playing up and after several hours poking around under there i found the fusebox wet.)
Anyway, my point is - once water gets past the windscreen, that area is where your ventilation comes out. So lots of water + lots of air + cold glass = loads of condensation.
Keep looking, don't give up - you will find the leak.

[Poppy]

Why not just push the screen demist button...Clears mine on no time flat...:shrug:

[buchanan]

when is the last time the windows were cleaned,dirty windows steam up,try cleaning them.

[SD1too]

Any idea what the hell it could be?
Hello Kevin,

I'm glad that you've posted this because I get a bit of misting (not as severe as yours I have to say) when I select 'Econ' after using 'Auto' whenever the weather conditions are damp. I don't have any detectable water ingress either. I know that the HVAC intake flap is supposed to adopt the 'recirc' position when the ignition is turned off to prevent humid air entering the cabin and I keep meaning to check this. Singvogel's suggestion of a heater matrix leak sounds plausible, but I'm as puzzled as you are. My SD1 has never done it and my wife's hatchback doesn't either (both have a.c.), and it doesn't seem to affect all 75/ZTs. If you solve it, please let me know.

Simon.

[Kedaha]

Not a heater matrix leak as I had a look at it when I removed the clutch pedal to get rid of an annoying creak. I guess I'll take out the glovebox and get the passenger carpet up a bit and see if there is water there!

I did have the windscreen replaced, and they didn't do an amazing job on the seals - but that was 14months ago and the problem only started occuring 6 weeks ago :/

[HarryM1BYT]

Hello Kevin,

I know that the HVAC intake flap is supposed to adopt the 'recirc' position when the ignition is turned off to prevent humid air entering the cabin and I keep meaning to check this.
Simon.

In a quiet location, you should be able to hear the flaps close when you turn the ignition on and off. It doesn't prove the flaps actually close, but it does confirm the motor is running.

[Kedaha]

Ok, no water under passenger carpets. Checked sunroof drains by pouring water down them - all drains seem to clear quickly under the car. Checked the front passenger drain behind the glovebox and it's good. Going to tape up all the windscreen seals next and see if that helps at all and also get up the drivers carpet(when it stops ****** raining!)

[xStevex]

This was happening me, my cabin/pollen filter was sitting in a flooded plenum and when I drained the plenum and replaced the filter the problem was cured.
Worth checking? :shrug:

[Dashiel]

Going to tape up all the windscreen seals next and see if that helps at all and also get up the drivers carpet(when it stops ****** raining!)

what i advise is after it has rained heavily get in car with some slither of tissue paper and get it in any cracks around the windscreen where water would flow. that is sides, and top and bottom corners. you will not see the water - it will be a slither, sometimes behind the inner seal - so use the tissue to get in the cracks to try and blot it out. if the paper comes out wet, then there is your problem. you can use the technique elsewhere as well. believe me, seeing water in a dark car in winter is not easy.

[beinet1]

Hi,

I have the same problem as the treadstarter. Can not fins any moisture in my carpets. Could the drain tubes to the A/C system be blocked or partially blocked so the drain water mists up the windows when the A/C is turned off???

[ASHEEN]

I think your AC Compressor has failed, or your air con needs regassing. The compressor is a good way to demist your windows. It will work with your econ off. Ie, when there is no econ on display, your compressor is on or should be.

Cheers

[SD1too]

Could the drain tubes to the A/C system be blocked or partially blocked so the drain water mists up the windows when the A/C is turned off???
Yes, that's possible. You can rod the tubes from beneath the car. You should also see small pools of water from them when the car has been standing after the air conditioning has been in use.

Simon.

[beinet1]

I think your AC Compressor has failed, or your air con needs regassing. The compressor is a good way to demist your windows. It will work with your econ off. Ie, when there is no econ on display, your compressor is on or should be.

Cheers

Hi,

My A/C is working very well, and this is not a problem when its running. The problem occors on ECON mode or when the outside temperature is below the A/C systems operating limit like 1-2degree C.

[bl52krz]

Yes, that's possible. You can rod the tubes from beneath the car. You should also see small pools of water from them when the car has been standing after the air conditioning has been in use.

Simon.
I think you need to be very careful about "rodding" the drains from the aircon system under the car.I think you will find that thee are little flaps in the pipes so far up, to stop anything "going backwards" up the pipes.

[SD1too]

... there are little flaps in the pipes so far up ...
You're right about the flaps Dave, but on my car they're mounted externally at the open end. Is yours different?

Simon.

[kaiser]

The result with steam after using AC is quite understandable.

Moisture will condense if it hits a colder surface than ambient air, provided it is close to saturated. Hot air will absorb more moisture than cold air.

The demist function of the car uses maximum cooling with the AC. That results in a sharp decrease of the temperature of the air passing the AC, and moisture being extracted from the air, and expelled through the two drains under the front seats. After passing the AC, the cold air then enters the heater, where it now becomes hot as well as dry, and is passed over the front screen. That dry air will absorb a lot of moisture, resulting in very rapid drying of the screen and thus removal of the moisture.

With the cabin recirculating button activated, there will be a continuous drying out of the air in the cabin. The only contributors to moisture in the air is the perspiration/breathing of the occupants as well as any moisture from wet clothes, and, in this case, wet carpets!

When you switch the AC off, there will be a lack of condensation and draining of the air, and your windows will start to mist up again. The colder the window, and the more moisture in the car, the worse it will be.

[SD1too]

I fully understand your explanation. However, when conditions get to this stage:

With the cabin recirculating button activated, there will be a continuous drying out of the air in the cabin.
... there will be very little, if any, moisture content to be extracted. Clothes will be dry leaving only a very small amount of humid air from occupants' breath. So why, when 'Econ' is selected, do all the windows steam up? Where is this moisture suddenly coming from?

I have noticed this phenonemon with my 75. It doesn't happen with the other two cars in the family. It happens only following use of the air conditioning, sometimes when the car is next used hours or a day later! If I persist with Econ mode, and take drastic conventional ventilation measures, the mist eventually clears. It does not then return, even with the same occupants continuing to breathe and the ambient conditions remaining the same.

This does appear to suggest that the condensate from the evaporator is not being dispersed and humidifying the air when the system is next used in Econ mode. Furthermore the lack of complaints on the forum indicates that only a few cars are affected.

We know that leaves and other organic matter tend to collect in the chamber housing the air intake. It occurs to me that following rain this will ensure a supply of humid air to the car's heater. If air con. is selected it will be removed, but the Econ setting will transfer the moisture to the cold surfaces of the car's glass. Another possible explanation perhaps?

Simon.

[kaiser]

There will be residual water in the AC, maybe even lodged as ice on the evaporator or left behind after drainage in nooks and crevices.
That the system does discharge water is evident to anyone who has parked the car after use of AC, and seen the puddles under the car.
However it is entirely possible, even perhaps evident, that some considerable amount of moisture remains in the AC unit, thus indicating the drainage is not complete.
When recirculating the air, the flow path of the air must lead over these remnants of water (as the path is the same, just not with AC) which will then be brought into the cabin, or, or in addition to, when recirculation is used, the air goes through the pollen filter. It is quite often that the pollen filter is damp or wet at the bottom, or maybe even on the element itself, following rain. When AC is selected, this moisture is lost during cooling before it enters the cabin and you will not notice this. With the AC switched off, the air will pick up the moisture, and you will feel the increased humidity, which will gradually build up inside the car, as the same air is cycled repeatedly.
If you switch recirculation off, the path of air will come from the outside, and have normal humidity usually drier.

[ASHEEN]

The compressed air from the air conditioning demists the windows effectively. I have the same problem on my Sharan, without the AC on, it mists up, so I have to have the Compressor on to keep the front and side windows demisted. Seems normal to me.

The Airconditioned air dries out the condensation.

[Kedaha]

Just to update this -> I put alligator tape at the bottom of each A-pillar where the windscreen seal wasn't the best and since then, I can keep the car condensation free just using econ with fresh air from outside. I'll take a pic of where I taped tomorrow, just in case anyone suffering similar problems wants to try it themselves.

[MrDoodles]

This might sound daft, but my ZT did exactly the same when I bought it and it was down to a swimming pool in the spare wheel well, caused by a split rear light gasket.

Once I dried out the boot carpet and stopped the leak, everything's been fine!