18

Before you comment, read below to see what I've done and why most answers are not helping me. Also, my native language is not English, so I apologise for not using the proper words.

I have an old Volkswagen Polo (2006) that has heavy condensation on the front window inside the car during autumn and winter. It’s that heavy that when the temperature drops below 0, the condensation will freeze and the inside of my front window will be frozen, making it difficult for me to start in the morning since I lose a lot of time.

Reminder that I have no option to use a garage. I have no issue if I can park my car in the garage, but this is just not an option at the moment.

Things I've tried, but didn't produce any results:

  1. Checking if my air conditioning works: it works perfectly. A few days ago I deliberately had my windscreen fogged at a very low temperature. As soon as I turned on the air conditioning at a low temperature, the problem was solved. This indicates that my A/C is working and it should be drying the interior air.
  2. Water in the car: checked the most frequent places (such as the mats on the driver's & passenger's side at the front and rear; in the back of the trunk; ...). No wetness whatsoever. Also no problem that water gets in through the doors.
  3. Moisture absorbers: these do work (you see a discoloration), but the problem of condensation persists. Assuming that there is an ongoing problem.
  4. Leave air conditioning on to get the cabin as dry as possible: no effect. I have no issues during driving (see point 1), but as soon as I've been parked outside for a long time (say 12 hours at least), there's another severe form of condensation on the inside of my windscreen. It's not damp like other cars, but a form of water.
  5. Clean the front window: tried this. Seems to work a little bit but not much and not for long.

It looks like I'm out of options. There might be humid air coming in, but I assume since air comes out, it can also go out and that would solve the condensation issue. I've tried to leave the window open a crack, and this resulted in no condensation, assuming that proper air flow does work, although not an option when it's raining or snowing.

The car interior is also "quite" hot for this time of the year.

How could I possibly fix this?

  • 9
    The water is coming from SOMEWHERE. You claim to have ruled this out but I suspect you have missed something. Find where it's coming from, eliminate the source, and your problem will be resolved. I'm with the "water in the car" camp. – jwh20 Nov 11 at 17:05
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    @jwh20 Thanks for your reply. I suspect this is the case, but I just can't find any sources of water in my car. Do you have a list of places that I should check that are maybe not that obvious? – Rob Nov 11 at 17:13
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    Just in case: Running the aircon on full regrigeration AND full heat and max air flow - if the system allows you to. Will give best results. || Try (does no harm, may help) a low power fan blowing air across the window during the night. || Calcium Carbonate dessicant (drying agent) is very cheap and can be reconstituted by heating when it gets wet and slushy. A substantial line of this in a long thin container at base of windscreen may help. ... – Russell McMahon Nov 12 at 9:52
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    About 25 years ago I had a 1982 (no air-con) VW Polo with the same problem. Sometimes I would have to drive with my head out of the window until the windscreen cleared. In the winter I basically had to drive with the windows open. I was glad to get a new car! – Aaron F Nov 12 at 10:37
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    @Mawg You probably should mention that he should use clean cat litter... – Oscar Bravo Nov 13 at 12:19

14 Answers 14

31

Check the A/C drains are not blocked. The A/C condensates moisture from the air at the evaporator behind the dashboard. If the drains are blocked you will have a pool of water there ready to evaporate. The moisture will go up through the vents and condensate on the front windscreen.

You will need to look under the car approximately under the dashboard. There may be one or two open rubber pipes or holes as @Al_ says in the comments. You may need to poke something in the pipes to clean them out. Preferably use something plastic like a grass strimmer cord.

This video may help identify the location of the A/C drains.

  • 3
    Thanks @HandyHowie. Just wondering if it's easy for a beginner to spot this? I don't have any experience with cars beside the basics, so I wonder if the job is easy to do after watching some Youtube vids/pics on Google. – Rob Nov 11 at 18:13
  • @Rob It's usually on the bottom part of the firewall. Approaching the car from the front, usually on the right side for a left hand drive car (think of Ireland and the UK), and on the left side for a right hand car. It's either an hole or a distinct hose – Al_ Nov 11 at 19:28
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    You will need to look under the car approximately under the dashboard. There may be one or two open rubber pipes or holes as @Al_ says. You may need to poke something in the pipes to clean them out. Preferably use something plastic like a grass strimmer cord. – HandyHowie Nov 11 at 21:46
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    This video may help - youtube.com/watch?v=DfXyo7a2F9A – HandyHowie Nov 11 at 21:50
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    Unfortunately, i just noticed i mixed things up a little in my earlier comment. I actually meant "right hand drive car (think of Ireland and the UK)" and "left side for a left hand car" – Al_ Nov 12 at 22:24
16

I think the point everyone else (and you) are missing here is if the weather is cold enough the temperature of the windscreen is below the dew point, your breath has enough moisture in it to do exactly what you're talking about. If the windscreen is below freezing, then your breath will first condensate there and then freeze. This lends perfectly well with your description as well as with the fix of running your AC to solve the issue. This is one of the purposes of your AC unit is to remove the moisture in the air during the winter months to prevent this exact problem. In other words, just run your AC and your problem is solved. Besides, your AC unit needs to be ran year around to keep it lubed and functioning correctly. Believe it or not, it will run/last longer by doing so.

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    Hey @Paulster2. I totally understand what you mean with this. I just find it odd that, even when I left the car and it was totally clear and dry, the windscreen still condensates before I even enter the car the next morning. The windscreen is already completely frozen on the inside when I enter the car. Also, running the A/C when it's completely frozen won't help. Trying to get heat when this car is idling after a cold start takes ages! As soon as I take off, it starts heating up within minutes so no issues there. – Rob Nov 11 at 18:28
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    @Rob - Something you can do to help with this is to use a product like Rain-X Anti-Fog (no affiliation). It will prevent some/most/all of whatever moisture in the vehicle from collecting on the treated area. Just a thought. – Pᴀᴜʟsᴛᴇʀ2 Nov 11 at 18:36
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    The things i listed is where i would look into carefully. Do you periodically check the coolant level in the header tank? Have you been having any issues with the engine coolant level lately? Do you get a smell sweet at the air vents? Can you see the condensation dripping from the firewall when you've run AC for a long time in a wet day? – Al_ Nov 11 at 20:15
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    @Al_ +1 to the advice for coolant check. I once had exactly the same problem: the car would just never warm up while idling. The reason? Leaked coolant. – IMil Nov 12 at 3:47
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    @Rob Your front windscreen has condensation on it in the morning because your car cooled down overnight. This forces the moisture in the air to condense out somewhere, and it preferentially condenses on the windscreen because that is the coldest part of the car. – Martin Bonner supports Monica Nov 12 at 11:06
15

If you can't find the source of the moisture, you can use a work around.

You say there isn't a problem if you leave the windows open a little to ventilate the car, but it lets in the rain. A solution to that is to fit wind deflectors. Although intended to deflect wind, you can leave the windows open an inch without rain getting in.

The stick-on kind aren't always rain proof (it can trickle past the adhesive). The ones that tuck into the window groove work well. Fitting them to the front doors only might be enough to give adequate ventilation.

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Besides this particular problem, they allow you to drive the car in the rain with the windows partly open. I like the feel of naturally moving air and the ventilation it brings, and it make me feel less insulated from the world outside the car.

12

You say that when you close the car, the air inside is dry.

This might be the case, but cold air can hold significantly less water vapour than warm air. That is, the same air which was "dry" when you have closed the warm car will become oversaturated with water once it gets cold. And this extra moisture will condensate on those parts of your car which cool down first: unfortunately, the windows. I emphasize: no extra water needs to be added to create the condensation. You said "The car interior is also quite hot for this time of the year"; well, the hotter you keep it while you drive the more vapour there is to condensate.

The easiest, though a bit time-consuming way to handle this would be to let the car cool down a bit with open windows or even doors. You could also try to keep temperature a bit lower while driving.

To make things worse, the airflow in your car might be obstructed, check the cabin air filters. And, to state the obvious, I hope you don't leave the air recirculation turned on.

Finally, based on your comment "Trying to get heat when this car is idling after a cold start takes ages! As soon as I take off, it starts heating up within minutes", I support Al_'s suggestion to check your engine coolant level. Though if your car's a diesel, it might be natural.

  • Hey @Imil. Thanks for the answer! My cabin air filters has been replaced last year and about the coolant. I meant that when I have a cold start (like in the morning before commute), it takes a while for the car to warm up. Isn't this normal since the engine isn't running and it gets no heat? Also, coolant level has been stable for a very long time (I check it about monthly). – Rob Nov 12 at 5:54
  • It' important to note that warmer air isn't inherently more humid, it just has a greater capacity to hold water. So you're welcome to (like me) bake in your own car, just so long as you keep re-circulation off to pull dry air from outside, and/or turn on the AC with heat to dry out the air as it enters the cabin. – bracec Nov 12 at 16:20
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    What I do in winter is to heat the air in the car. A few minutes before I arrive I turn off the heater and open all my windows to replace the hot air for cold (less water containing) air. – ffonz Nov 12 at 16:52
  • @Rob I can't say for sure what's normal and what's not. Certainly it takes some time to heat the car, and certainly longer while it's idling and the engine's not too hot. But when my car did have low coolant, it could literally run idle for 15 minutes and not warm up the windshield. If you just run it idle for a couple minutes, then it's probably OK to still be cold. – IMil Nov 12 at 23:45
7

We had a Ford Ka that constantly fogged up as you describe. It turned out to be a badly fitted windscreen that leaked water in slowly. We tried to patch this by putting in the sealant around leaking areas but in the end, a new windscreen was the solution for us. Finding that there was water getting in was very hard and took weeks of effort.

We could not find any signs of water inside the car until a sustained period of heavy rain (days of it) at which point one of the front footwells became damp. That lead us to understand it was the front of the car that had the main issue. What followed was me pooring large amounts of water over bits of the car until any sign of water coming int happened. We spotted a few drips and tried to get a better look when I next repeated the test. Then we knew where I poured water to get it to come in.

After this we started to try and apply more and more sealant under the rubber gasket of the windscreen to stop the water. We did manage to reduce it eventually but not stop it entirely. Finally when the windscreen got a few chips that could be repaired we got it replaced instead as it was not a high cost. Turned out that it had been replaced previously but instead of having adhesive all the way around where it sits, it had a few blobs of it along the edges, hence no watertight seal.

It needs only a small amount of water to get in a car regularly to cause massive issues with damp and misting up. Dring out the car can take days or weeks in cold weather. I expect you have a small leak into the cabin that could be anywhere, even behind the dashboard.

5

The trick is to get rid of the moisture when your car is nice and warm.

When you park at the end of the day, open the doors (or windows, but doors are faster) for a minute and let the warm moist air escape, otherwise all that moisture will condense on your windshield as it cools down.

Source: Live in a cold climate

4

Cover it

Cover the windscreen on the outside with a small tarpaulin, or an old bedsheet. Weight it down on the roof, and on the scuttle. Do not trap it with the wipers.

The idea is to keep subzero draughts away from the outside so that it doesn't chill the glass. This prevents condensation from forming on the inside. Used reliably in Northern England for many years.

3

The condensation occurs because there is a difference between the temperature of the air inside the car which has enough humidity in it that when the temperature of the air outside drops, and the wind blows, the windshield temperature drops faster than the air inside the car. When the windshield temperature drops to the dew point, the water condenses. When you leave a window open, it allows the temperature of the air inside to drop with the temperature of the air outside, and the differential between the windshield temperature and the inside air temperature is not enough to reach the dew point.

To fix the problem you need to insulate the windshield from the outside air so that the temperature can’t drop rapidly. Put a blanket or a towel on the outside of the windshield overnight, and observe the difference.

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    To back this up, many (or probably most) motorhome/RV/camper-van owners in the UK use external insulated covers on the windshield when they are parked. We just bought some for our motorhome, and condensation on the inside of the windows was reduced to almost nothing. – Graham Nov 12 at 14:07
  • @NL: thanks! Would something like this work fine? tuinadvies.be/shop/foto/sizes/… – Rob Nov 12 at 16:41
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    Also, what about if 'in theory' I would place a cover like that on the "inside"? – Rob Nov 12 at 16:52
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    If you also placed a cover like that on the inside you would not get condensation because moist air would not be coming in contact with the windshield. However it would be more difficult to place a blanket on the inside because you are fighting gravity. A sun visor would help reduce the air flow against the windshield as well. – NL - Apologize to Monica Nov 12 at 16:55
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    You need to learn BLUF :-) I only added my answer because a quick skim of other answers didn't look like anyone else had advised the same thing. – Rich Nov 12 at 16:56
2

This points to moisture being in the car interior. It may not feel wet, or have obvious visible water but when you have moisture buildup in the car like that it's rarely anything else. You need to start looking at your seals to find the ingress point.

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    I assume that the seals might be a big factor in this problem, especially since it's an older car. Is it for a newbie easy to spot where the problems are (and how) and would the cost of reparing these seals be high given that it's quite an old car? – Rob Nov 11 at 17:31
  • Seals are often easy and cheap, but it depends. – GdD Nov 11 at 19:22
2

If my understanding of water is correct, this is happening because the moisture in the air is condensing on the (relatively) cold window.

Try putting up a reflective sunscreen on the front window. This will do 2 things. It will make it more difficult for moisture in the air to get to the window. It will also reflect heat back towards the window, keeping it relatively warm.

Using a matte black sunscreen would even work better, in theory. The sun will shine through the window, heating the matte black surface, and thus warming the area between the window and the black sunscreen. (You may have to paint a regular sunscreen black to try this)

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    A matte black surface will cool down even more overnight. On a clear night, it will be trying to reach equilibrium with the night sky which is very cold. – Martin Bonner supports Monica Nov 12 at 11:08
2

Some certified tips from someone used to living north of the polar circle.

  1. Avoid all sources of water into the car. Are the mats wet? Take them out when you exit. The fluff you scrape off the windows in the morning? wipe it up, get it out. Ensure that you and your breath is the only source of water. (that is still too much, but unavoidable)

  2. Clean your windows, thoroughly, on the insides with a non-staining window cleaner. Finish last with isopropanol wipes. Dirt and smear promote sites for condensation, the condensation becomes ice. Water left to dry leaves mineral/carbonate residues, those also promote condensation.

  3. When you run your car, do not circulate air in the car, always run air through, if air quality outside allows for it. If weather allows, keep a window slightly ajar while driving.

  4. When you run your car, wear jacket and mittens and have a colder than you normally would. Warm is very nice, but warm air holds massive amounts of water, all of which will deposit on cold surfaces, eventually. Reduce it to minimum within comfort. This is also a life saver in certain outside conditions, having a hot car in cold snow and wind is like begging for ice buildup on wipers and window - not nice if you cannot stop (for instance if you are being convoyed, a common enough happening in the north)

  5. If problem still occurs - there is a final step you can take. Mats on the windows (outside) will slow down thermal transport and make windows much less icy on both sides. Windows will not be the "cold face" of the car and water will seek to condense elsewhere. Store the mat in the boot, you dont want it soggy when you put it back on the window. Secure the mat with your wipers.

  • Thanks! I'm already doing 1, 2, 3, 4 (I use about 18 degrees celsius). I've been thinking about 5 and I guess it makes sense, but I only use it to prevent ice buildup on the outside. Why does it work well for the inside also? – Rob Nov 12 at 16:40
  • @Rob 18 is lavish. 12 is much better. Lower if your hands are protected. It works because it isolates.water wants to condense and freeze on cold surfaces that can transpersonal the heat of freezing out to the environment. A mat slows the heat flux. – Stian Yttervik Nov 12 at 17:03
0

If the a/c is working then it collects the moisture inside the car and deposits it outside.

As that is not happening you need to check why.

And the a/c on my car runs winter and summer 365 /365... keeps the interior dry.

  • so you're saying the A/C does collect moisture, but it doesn't deposit it outside as opposed to a normal A/C? – Rob Nov 11 at 17:59
  • No need to "check why" as OP already said why—the car was parked and not running. Also, when cold enough to freeze as OP said, he obviously would not be running the AC. – WGroleau Nov 12 at 19:03
  • @WGroleau I have read the manufacturer's instructions & workshop manual... even when cold enough to freeze a/c still runs as necessary to hold the interior moisture level within limits. – Solar Mike Nov 12 at 19:07
  • @SolarMike Even in very cold weather (below freezing) all it may take to let the compressor engage is actually warming the engine bay up. In rare cases, the compressor operation might be tied to an ambient temperature sensor. In most cases, it's just a pressure switch or transducer either located on the liquid line or on the receiver dryer, on modern cars. So all it takes for the compressor to operate is a warm enough engine bay. In that case, the compressor will either cycle on and off frantically or operate with the minimum displacement it can (and get noisy), however. – Al_ Nov 12 at 20:47
0

You have no problem when you can park the car in a garage. Therefore the problem is 100% related to parking outside in the open.

My boy's car was outside for months, and suffered from bad condensation on the inside of windscreen. Turned out the car faced south (away from sun) and the windscreen got coldest. There was water pooling in the spare tyre well, at the other end of the car, due to a leak in the boot seal.

So your problem is that water is entering the car's cabin when parked up

If you can possibly do so, get a garage. Your car will start better, run more efficiently, and the paint will last longer. I can't understand people who part nice new cars outside in all-weathers. Your "old" polo will absolutely benefit from cover.

To dry my boy's car we plugged a domestic dehumidifier in, and left it in the passenger seat running on High for days. The fog dropped off, but a week later it was still pulling a couple of cups of water from the upholstry a night. The mains power cord simply slipped through the rubber door seal without issue.

A carport is a good solution too - better than nothing without the full expense of a garage. A car cover may help if that's all you can afford.

-1

When the car is in motion, all occupants are breathing warm moist air into the car. When you park and close it, most of that air is still there and can’t escape. The cold outside then chills the glass, which chills the air closest to it, causing it to release the moisture it contains—onto the glass.

That's why opening the window a tiny bit helps. If wind blowing in rain/snow is a problem, one way around it is figuring out a way to ventilate without draining your battery. Perhaps some sort of awning that you could wedge into an almost-rolled-up window. Maybe include a battery-operated fan that can be recharged from your circular power port (the former cigarette lighter).

I once saw a solar-powered set of fans that could be put in a window that way. Don't know the source nor whether still available.

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    Welcome to the site! This seems like accurate and useful information (though others have given this exact information) but it doesn't provide any answer. Please consider either updating to provide an actual suggestion of a course of action to improve the problem, or it might be best to delete your own question. – ErikE Nov 12 at 17:35
  • I posted it because I did not see that explanation when I scrolled through the comments. I edited in a proposed solution. – WGroleau Nov 12 at 19:01
  • Given that the A/C dries out the air in the cabin and that I've tried airing the car out multiple times while driving, why would this still happen? – Rob Nov 12 at 19:16
  • If it is actually true that AC is supposed to dry out the car in winter, than as Solar Mike said, obviously it isn’t doing so. If not (or if you choose not to fix it), here are alternate solutions. – WGroleau Nov 12 at 20:16

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