Windows fogging up INSIDE car

windows

#1

The windows in my car, a 1997 Cougar, have recently started fogging up inside. It only started doing this for the past week week and a half. I’ve checked the carpets and they’re all dry. My car is the only one in the parking lot with fogged up windows. What do I do?


#2

Check your radiator to see if its level is dropping. Only open the cap if the engine is cool. Sounds like your heat exchanger is leaking. This has the radiator fluid circulate through it and provides heat in the cabin area. Fogging of the windows and the age of your car point to a leak. Do you notice a sweet odor-antifreeze can smell sweet. Best of luck as these can be a PITA to replace.


#3

+1 to Steve’s comment.
If the carpets are dry, it is very likely that the heater core (or, as Steve refers to it, the heat exchanger) is leaking.

In addition to the problem of fogging windows, this is a potential health hazard, as coolant leakage into the HVAC system causes you and your passengers to inhale aerosolized coolant–and that isn’t good. I developed some really nasty lung problems as a result of that issue with my '86 Taurus.

Hopefully the heater core on the OP’s car is easier to replace than the one in my Taurus, which necessitated removing the entire dashboard and some other parts in order to gain access. The labor cost for that job was…really high.


#4

Does your windshield have a film that smears when you try to clean it? That’s the other usual sign that it’s coolant.


#5

In th event this is not related to a weepy heater core which is causing an engine coolant haze on the glass you might consider an A/C problem.

The A/C compressor should be operative in the DEFROST mode as that will dehumidfy the air inside the car and prevent fogging.
With the engine running and the mode control on DEFROST you might pop the hood and make sure the A/C compressor is engaged.

Even if engaged a low state of refrigerant charge could lead to foggy windows. Also make sure sufficient air is blowing through the DEF ducts.


#6

the simplest thing is to first verify you didn’t leave the heater set to RECIRCulate…


#7

Make sure your heater/AC is set to “fresh air” and not “recirculate”.


#8

This car may have EATC on it.


#9

‘Make sure your heater/AC is set to “fresh air” and not "recirculate.’

That is an excellent point.
I have been astounded over the years by how many co-workers and neighbors had their HVAC set to recirculate, and–as a result–were plagued with fogged windows.


#10

Nothing to add - every possibility has been well described above.


#11
I've checked the carpets and they're all dry.

Have you checked the spare tire well?


#12

@GWalcott, where do you live? I was in Utah last week and I had ice on the inside of the windshield, but none on the outside. I spent 2 hours driving from the airport to my destination, and I think I humidified the air inside the car during the trip. The low was like -16 and the high was -3 the next day. It only happened once. The SUV was a 2016 Escape, and I doubt there was a problem with the heater.


#13

When my heater core went, the carpets were never wet but the car got so fogged up inside just coming back from NAPA, I couldn’t hardly see to put it in the garage. You should be able to smell the antifreeze though inside the car.


#14

The above posts cover the most likely causes. Besides that, here’s a couple of other ideas, not very likely, but something to consider anyway. I once had an inside fogging problem caused by water getting under the carpet on my truck. A drain had plugged up, causing rain water to overflow and get into the cab instead of pouring out through the drain system to the ground. The top of the passenger side carpet felt dry, but there was water below the carpet underlayment. Another time it happened, this time in my Corolla, I finally figured out the reason: I had started to drink a cup of coffee during my winter morning commute, and the steam from the coffee was causing the windows to fog up.


#15

Lets assume that your heater core is not leaking and you do run the defrost with the AC on to dehumidify the cabin. But the fogging occurs when the car is parked as implied by the statement that it is the only car in the parking lot to do this.

My conclusion would be that the evap drain is clogged up. The AC is removing the moisture from the air while you are driving, but the water is accumulating under the evap coil and not draining out. Now after you shut down, your warm car begins to cause that water to evaporate into the warm cabin air where it condenses on the cold windows.

In the summer when the air can hold a lot more water vapor, if this drain plugs up, you will get enough water to overflow out onto the passenger side carpets. But in winter, the air will typically only have 10 to 30% of the water vapor in it that it has in summer, depending on where you live, so the tray below the evap coil may not fill up.

The evap drain is easy to clean. If you have a regular mechanic, he may do it for free, but it will take at least 10 minutes for him to get out the air hose, crawl under your car and blow out the obstruction. He deserves some compensation for that. If he has to put it on the lift, then with the moving of the car, the paperwork and adjusting the lift points, he is into it for a half hour, even though the actual clearing takes only seconds.


#16

I bought a used 1984 Chevy Cavalier wagon that had been “steam cleaned.” The carpets and padding were very wet and with winter coming on, the insides of every window had frost on them every morning. Besides parking it in the sun with windows cracked open, I put an electric heater in it for a few nights and the interior moisture finally was driven out.

As far as driving in Recirc mode: my 2007 Chrysler Town and Country will not allow the Recirc mode when the defroster is selected: if I push the Recirc button, it blinks 3 times and does not activate the Recirc mode. Also, if the heater or AC (not defroster) is set in Recirc mode, once the car is shut off and turned back on, Recirc mode has been deactivated.

It’s the newest car I had owned. Do a lot of other newer cars have similar logic in their HVAC systems?

I think it’s a good feature for the great numbers of drivers who do not read and understand their owners manuals, and end up driving in Recirc mode, not realizing how that affects their outward visibility, therefore their safety.