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Major Moisture/Fog Problem in Car

Hello all. Thanks for reading.

I’ve recently run into a problem with my car, after it was taken into the shop a bit ago. I live in Ohio, and the weather here is cold. Now that I need my windows defrosted constantly, I’ve realized that my car is always fogged with tons of wet moisture that sometimes freezes on the inside.

In order to have any success or effectiveness, I have to have my heat cranked to the hottest setting at full blast, which makes the car uncomfortably hot. But even with such drastic measures, my windows are still super foggy and wet. My back passenger windows are always 100% fogged no matter what, it just happens right away within a minute or two. My front windows are always half fogged, and only small ovals right by the side defrost blower work. I have to roll down the windows constantly to wipe them, but it returns within a few minutes.

I’ve tried all the settings in my car. I’ve turned on the AC as I heard that can help temper moisture but to no avail. I’ve tried putting air from outside vs. cycling it and there’s no difference.

I’ve had this car for years and I’ve never had this problem. What could possibly have changed? How do I combat this? Thank you.

Is there any place in the car where the carpeting is wet, or damp? If so, you may have a leak from the front or rear window, a sunroof drain or the AC drain. Even if there is not wetness on the carpet, your AC drain may be clogged. It can usually be reached from under the car and cleaned out. So, might take a shop with a lift.

I have lived that problem in Ohio winters. My first car had that problem like crazy. Never really fixed it.

The most likely scenario is that someone–either you or somebody at the shop–activated the “recirculate” function on your HVAC controls. Please check those controls, and then let us know your findings.

If that proves to be fruitless, then we might be able to advise further measures to take if we knew the make, model, model year, and odometer mileage of your mystery vehicle.

What work did the shop do? Did they also shampoo the interior?

A leaking heater core will cause your defrosters to fog your windows, but you say that the moisture freezes up on the inside. That points to the A.C. condensate drain being plugged.

A leaking heater core would cause fogging of the windows but it wouldn’t freeze. That’s because coolant contains, well, antifreeze.

Let me ask you this. Is the setting on the vent controls set for outside air, instead of recirculated air?


I am constantly amazed by the clueless people in my area who drive around in the winter with their HVAC system set to “recirculate”, and are then puzzled by the chronic fogging/freezing of their windows.

Over the long run, fresh is better than recirculate for this problem. First you need to dry out the insides, probably using an electric heater with windows open a bit, and also outside in the sun.

That is all true, but we still have no clue as to…
Model Year
Maintenance record

Until the OP fills-in those blanks, it will be difficult to provide help.

This is a pretty generic problem, and that info is probably not relevant. Still, it could provide a clue I suppose. I wonder if the work done on the car has some bearing on this problem that showed up after it was in the shop. Did the shop sheepdog sleep in it, or worse, and they shampooed the interior before returning it to the owner?

What work was done and have you talked to the shop because apparently you did not have this problem before or last winter if you had the vehicle then.

So may questions…
So few answers…

Turning the speculator up to 11 pretty soon now!

It sounds like there’s a new water source in the car somewhere. OP should check the carpets in both the front and rear seat for signs of dampness. Often it is necessary to pull up the carpets a little as water can get underneath the under-carpet pad sometimes . Also check the trunk especially the place where the spare tire resides.

Feel the fog on the window surface . Does it feel more or less like water, or does it feel more slippery than water? If the latter, there’s a likely problem with leaking coolant from the heater core area. If OP cannot find any source of water, maybe something the shop did, or in the shop environment that just saturated everything in the car interior with 100% humidity. If that’s the case opening the windows as the car sits overnight will eventually clear-out the interior fog problem.

However, I’m guess the work the shop did was to the rear tail-lights and they didn’t get that area sealed correctly, allowing rain water to get inside the car there.

Hi All, THANK YOU for replying! I’m sorry that I didn’t get back to your ideas and inquiries right away, I don’t get on the computer much with my schedule. I’m going to address all of your ideas and questions:

First: Car Info. Sorry I didn’t provide it initially.
2007 Kia Optima
Mileage is approx 100,000

Mustangman - There aren’t any wet or damp spots on any of my car interior surfaces.
VDCdriver - I’ll check the HVAC and get back to you guys. I’ll have to look it up on youtube, but I’m assuming it’s not too difficult.
shanonia - there was no shampoo of the interior
Tester - Yes, vent controls are outside air.
George - Yes, it feels more slippery. And yes, I’ve had my taillights worked on. Is that a common problem?

Again, thank you all for your replies. Question, am I able to check the AC condensor drain and HVAC controls without taking it into a shop? And what do the rest of you guys think about the possibility of an unsealed tail light? Would there be water in there to prove it?

Assuming you have a covered compartment in your trunk for the spare tire, have you checked if there’s any water in there?

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