Windscreen steaming up??? Mk1 C5

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waynedance
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Windscreen steaming up??? Mk1 C5

Post by waynedance »

Any ideas why when I get in my car in this damp cold weather my screen is so misted up on the inside?

Pollen filter not to old, no water leaking in the car and aircon works fine. Should I be doing something when parked up like leave recirculation on or switch off ac a few mins before parking up.
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Re: Windscreen steaming up??? Mk1 C5

Post by Northern_Mike »

Yes. Mine does this.

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Re: Windscreen steaming up??? Mk1 C5

Post by myglaren »

Mine mists up when first started on a cold morning but clears quite quickly with the demist button.
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Re: Windscreen steaming up??? Mk1 C5

Post by Mandrake »

Try giving the inside of the windscreen a really thorough clean with something that leaves no residue - fogging can be much worse if the glass is contaminated (even if not visibly) as it gives the water molecules something easier to condense on.

But, to some extent its normal. If de-mist and wiping struggle to clear it it's probably dirty though.
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Re: Windscreen steaming up??? Mk1 C5

Post by Peter.N. »

Could be the heater matrix leaking - but I hope not.

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Re: Windscreen steaming up??? Mk1 C5

Post by Jeff »

My 2001 C5 mists up so I try to cover the windscreen in the colder weather, I use a very large piece of cardboard (this year made from 51" plasma tv box) this is sealed inside two big black council bin liners, the type they put in wheelie bins / drums. Taped up it lasts the winter and does not matter if a bit soggy here and there inside. Thats for early cold mornings going to work.

When driving around I put the heater on to really warm up the inside of the car then drop the windows to vent as much moisture as possible. If walking in puddles to your car your mats will have a fair drop of water on them so direct the heaters down and try to vent it out as much as possible. I repeat this as I warm the car up.

Little things like this will help reduce the early morning pain of a soaking windscreen though cant avoid it completely so have to hand from the pound shop a "chamois sponge" - excellent for a quick dry and smear free wipe and away you can drive, as long as its not "ice" inside.

When the weathers dry and you have a chance on say a weekend open some windows and leave the wind blow through especially the rear windscreen which attracts more than its fair share of condensation. I trigger the hatch lock with a small bar so I can leave it up with the light off from the start.

Also check the carpets and spare wheel for moisture / leaks. Recently I found a number of pints of water around the spare wheel so as the car is 2001 I just drilled some small holes in the floor and wont bother tracing the leak which is probably coming from around the rear lights, I've checked the hatch seals and cant see anything amiss.

Hope some of this may help you.
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Re: Windscreen steaming up??? Mk1 C5

Post by Stickyfinger »

Never had it (very wet) on my 2002 and do not have it on the present facelift car....I put it down to demisting in the morning with the Air Con and then nearly always having the window open a little. (cant stand the smoke :) )
or maybe my rubber is nice and tight....oooooh MatroN !
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Re: Windscreen steaming up??? Mk1 C5

Post by Fake Concern »

Put the air-con on as it has a de humidifier which stops the misting. I leave mine on auto all the time.
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Re: Windscreen steaming up??? Mk1 C5

Post by Northern_Mike »

Mine has a new pollen filter.

It has a separate "demist" button which turns up thr blower, puts AC and recirc on. It demists quickly.

The screen and all other windows are clean.

My issue is that water is getting in *somewhere* overnight and it's completely wet through - I needed kitchen towel this morning again to wipe the windows. Too much for a chamois.

Carpets are dry.



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Re: Windscreen steaming up??? Mk1 C5

Post by Northern_Mike »

Peter.N. wrote:Could be the heater matrix leaking - but I hope not.

Peter
I suspect it is in mine. Can't find any other coolant leaks and a sniff test shows no gas in the coolant. It must be going somewhere. ..
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Re: Windscreen steaming up??? Mk1 C5

Post by myglaren »

I think that you would smell it if the matrix was leaking - it is very noticeable!
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Re: Windscreen steaming up??? Mk1 C5

Post by Northern_Mike »

myglaren wrote:I think that you would smell it if the matrix was leaking - it is very noticeable!
It does hum a bit... sadly I haven't been able to smell anything much for about 2 years. Now I've had my nose fixed my sense of smell is returning. .
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Re: Windscreen steaming up??? Mk1 C5

Post by Mandrake »

Fake Concern wrote:Put the air-con on as it has a de humidifier which stops the misting. I leave mine on auto all the time.
Great tip - I assumed everyone knew about putting the air-con on together with the heater to demist car windows, but I guess not. :)

It only works when the ambient conditions are above zero though, and works best in the range of about 4-15 degrees ambient.

The way it works is the air flow is directed first through the air con then through the heater matrix. Cooling down moisture saturated (100% humidity) air of say 6 degrees to 2 degrees forces the dew point down from 6 degrees to 2 degrees, (the excess moisture condenses and drains out onto the ground through the evaporator drip tray and drain tube) the heater matrix then warms the air back up to the desired temperature but the dew point remains at 2 degrees, thus the humidity is lower than it would have been without the air-con enabled.

It doesn't make any difference below freezing though because the air-con will not run when the evaporator temperature is below about 2 degrees to prevent icing of the evaporator. But at those low temperatures all you need is heat anyway as the dew point is already low.
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Re: Windscreen steaming up??? Mk1 C5

Post by mooseshaver »

Mandrake wrote:
Fake Concern wrote:
It doesn't make any difference below freezing though because the air-con will not run when the evaporator temperature is below about 2 degrees to prevent icing of the evaporator. But at those low temperatures all you need is heat anyway as the dew point is already low.
In my previous cars and probably the current one, when temp is low and you press demist, the air con still turns on and you hear the usual clunk as in summer. What is the air con doing when it's too cold to run but still running? Is just moving the liquid/gas around ?
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Re: Windscreen steaming up??? Mk1 C5

Post by Mandrake »

mooseshaver wrote:
Mandrake wrote:
Fake Concern wrote:
It doesn't make any difference below freezing though because the air-con will not run when the evaporator temperature is below about 2 degrees to prevent icing of the evaporator. But at those low temperatures all you need is heat anyway as the dew point is already low.
In my previous cars and probably the current one, when temp is low and you press demist, the air con still turns on and you hear the usual clunk as in summer. What is the air con doing when it's too cold to run but still running? Is just moving the liquid/gas around ?
It may come on initially, but as soon as the evaporator (the one inside the cabin) drops to between 0 - 2 degrees (exact value depends on the car - using the Lexia I've measured about 0.5 degrees on RichardW's C4, and 2 degrees on my Xantia) the compressor clutch will be disengaged even though the air-con light is still lit on the dashboard. When the temperature rises a couple of degrees again it will re-engage.

If this wasn't done ice crystals would form on the evaporator and at the least block the air flow, at worst cause damage to the evaporator.

In practice this means that when ambient is only a few degrees above zero the air-con will come on but only in short bursts depending on how close you are to zero. Once you're significantly below zero it won't really come on at all for any useful time, at least if you have recirculate disabled so that it's drawing in fresh cold air.

If it's on recirculate the air going into the evaporator is from the cabin so a lot warmer meaning the air-con will run however the air in the cabin will already have a lot less water content so its not doing much once its been running for a few minutes except cooling the air down then heating it back up to blow back into the cabin. :)
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