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[mrjimbo]

The other day i went out in the car and decided to run the AirCon for a while as you do just to keep things from sticking up. I did about 40 miles in about an hour or so, mostly round town with a bit of motorway thrown in just for good measure. When i was about 20 miles from home i turned the AirCon off. After about 5 miles the windscreen and all the windows started to mist up and the further i went the worse it got. It got so bad that even turning the windscreen demister on i was unable to see where i was going. I pulled over and waited for things to clear, which they eventually did, which took about 10 mins and then carried on home.
When i got home i had a good look around but i couldn't find anything obvious, no leaks, no damp carpet anywhere, no blocked drain holes, the pollen filter is new and bone dry so no water lurking about there, no funny smells or anything like that and i haven't lost any coolant so i put it down to just one of those things.
I went out in it yesterday and it did exactly the same thing. So i checked all around again and still can't find anything apparently wrong. First time it was a nice sunny day but yesterday it was raining is the only difference.

Anybody out there got any sugestions as to what could be causing this or is this to remain one of the worlds great mysteries ?

[damage consultant]

your air con is ok the air in the car is dryer than the air outside once the cars humidity adjusts to the same as outside the misting will stop. its best to leave the air-con on all the time it helps reduce dampness and in winter windows demist faster.

[jonnycool]

Mine is exactly the same - it seems to mist up badly after having the aircon on for a bit, almost as if the aircon sucks up all the moisture and then releases it all when you turn it off. It doesn't seem to be as bad if you don't use the aircon, so either decide to put it on or off when you set out 

[mrjimbo]

It only seems to have started doing it recently which is why i was a bit concerned as i've always used it the same way,ie if it hasn't been used for a while i run it for an hour or so every 10 days or so, or when i remember. I've not had the misting up problems with it before at any time in the 21/2 years that i've owned the car.

[Omegadoha, Desert Member]

Must admit I used to have this problem on my Ford Scorpio three years ago. This was even after I had the matrix heater changed.

Once I let the car idle with a/c off and stood outside the car, windows remained clear. Within five minutes of sitting in the car the windows misted up. Unfortunately I never got to the bottom of it. I put it down to the way I was breathing.

[Turk]

It only seems to have started doing it recently which is why i was a bit concerned as i've always used it the same way,ie if it hasn't been used for a while i run it for an hour or so every 10 days or so, or when i remember. I've not had the misting up problems with it before at any time in the 21/2 years that i've owned the car.

10-15 mins a week should be fine to keep seals etc lubricated.
As long as it clears quickly with the A/C on, I wouldn't worry about it. Both my currect Mig and my previous did it.
Giving the inside of the windows a clean with a decent glass cleaner helps, and you could also use the various anti-mist products used on motorcycle helmet visors.

http://www.mandp.co.uk/productsList.aspx?style=0&kw=anti%20mist%20spray

[cmeonthemove]

I first had this years ago with an Escort Ghia. It always gets worse this time of year as it gets cold and damp outside. This time of year I always run in eco mode so aircon doesn't come on.

[mrjimbo]

OK thanks for all your replies

It seems to be a common problem then, i thought it was the start of something expensive about to make an unwanted apperance.

[feeutfo]

its climate controle, on most models, not an air con unit and a heater. Cc controles the climate in the car, if you turn part of it off, it wont work as designed, ie set it to auto select the temp you want and leave it alone within reason.

 Unless its a cold morning and misted/iced up etc, then obviously use the de mist setting and the rear screen and mirror heaters.

The ac part of the system has a de humidifier built in. You may well notice the car also feels humid and uncomfortable when it mists up, and dryer and more comfortable when you turn eco off(ac unit on). Eco saves so  little money/fuel it really isn't worth using, as your finding out.....

There are however some things worth checking to keep problem to a minimum, as mentioned check the car is dry inside, carpets etc esp the pass side front and rear foot wells, and that the scuttle drain, well below pollen filter hatch in scuttle pass side is clear and not holding water, and that the air vent in the boot cupboard drivers side is clear and not filled with crap.

 That done, set it to auto and controle it with the temp setting, all will be well :-)