Fogging windows

[SteveS]

With the onset of some cold weather I have had two opportunities to drive the Fiesta ST in the cold (it's my wife's daily driver). On both occasions there has been severe fogging of the windshield and the side and rear windows. My wife says that it has been this way since we started having cool weather this fall. On the Auto setting it appears never to turn to the defrost setting. If you press the button for defrost and floor and turn the fan to about 3 it will slowly clear the windshield but the side windows never clear more just enough to see the side mirrors. Pressing the Max Defrost button clears the windshield and a little more of the side windows (and cooks you out of the car with heat). The recirculate button is not pressed. Pressing the AC button doesn't seem to make any difference. There is no smell of coolant in the car, and there has been no drop in coolant level.

Has anyone else experienced this? Is there some place in the air intake for the HVAC that may be holding water? Maybe from leaf/debris? Is there an actuator that is not working?

 

[MattM]

You may have a water leak in your car. Check the rear spare tire well area for water. This results in more humidity in the car which makes it harder to defog windows

 

[SteveS]

You may have a water leak in your car. Check the rear spare tire well area for water. This results in more humidity in the car which makes it harder to defog windows

Yeah, checked that already. It's dry. My wife is convinced that it started when the windshield was replaced after being broken by a rock flying off a gravel truck. But I can't see any place where water is coming in when it rains or going through a car wash.

 

[Cneu]

Check the rear hatch area, where those lil cubbies are behind the rear tire well. You can pull the fabric liner out really easily to check. Mine leaks down from there to the back seat foot area. It doesn't really pool in the spare tire area. I just posted about this in the daily thread. https://www.fiestastforum.com/threads/what-did-you-do-to-your-fiesta-st-today.1441/post-526450

I've been chasing leaks for the entire time I've owned this car. If you have a lot of moisture on your windshield, you almost certainly have a leak.

in my experience it could also be a leaky heater core but you'd smell that. I also have a door leak on the bottom of the door, so you might check that. Blast it with a hose, see if any gets inside.

If you continually have fogging issues, then water is continually getting into your car. Depending on where the leak is, the water might be getting absorbed into fabric or some foam before you can see it pooling. This happens to my car in the spring. The foam below the passenger seat will be pretty soaked but there's no pooled water anywhere.

I'd recommend buying some desiccant(damp rid) and a holder made for it. The holder needs to let the water drip, so you need a suspended basket with a bucket under it. I'm having trouble finding a photo of the one I use. But really, i empty probably 2-3 cups of water out of mine every few days. It helps dry out your carpet and foam, too. Once those get wet they take weeks/months to actually dry out, which makes the fogging issue linger forever.

Use it and empty it every few days. It makes a huge difference. I'm pretty sure most Kroger's carry the lil thing I'm talking about. I see a lot of desiccant bags but that seems weird. Try not to spill any of the water on your carpet after it's been absorbed by the desiccant.

I put a bunch of heavy rocks in the bottom of my catcher thing to keep it from falling over. I put it behind my passenger seat.

 

[Zormecteon]

Two things to look for.
The first may sound odd, but it's easy. See if the spare tire well has water in it. The rear is know to leak and that's where it can collect. When I looked I had about 3" of water there!.
The second is that the blend door(s) may not be working. Since you haven't been driving it may ask her if there's been that telltale thumping when walking away from the turned off car.

Just a couple of ideas.

 

[Snrub]

My FiST has always frosted on the inside more than other cars I have owned. RainX makes an anti fog product that helps with fogging and it helps a bit with frosting.
I've always suspected the door and window seals are not high quality.

 

[Sam4]

My FiST has always frosted on the inside more than other cars I have owned. RainX makes an anti fog product that helps with fogging and it helps a bit with frosting.
I've always suspected the door and window seals are not high quality.

I think more than a few of us has rear / rear hatch leakage. Somewhere under the 'rubber' strip along the gutter? Sunroof seal/drain tube? Mine drips and collects on top of a weathertech mat thankfully, but from somewhere under the headliner. I wonder if the 'auto' setting keeps the 'recirculation' on as a default - that'll fog it up.

 

[SteveS]

With the mild weather this week I've looked through the back end of the car again. Not a drop of water in the spare tire well. No water marks anywhere from the roof drains, taillights, or anywhere.

I am wondering about recirculation too. The windshield clears but the side and rear windows stay fogged even if you go to manual max defrost and the recirculation is supposed to be off.

 

[Intuit]

Holding something like a paper towel over the various vents should help confirm that the air is being directed properly... at least at that moment. (they can get intermittent -- more likely to fail under frigid conditions) The paper towel should be moving vigorously or barely at all depending on the blower and vent settings.

the side and rear windows stay fogged even if you go to manual max defrost and the recirculation is supposed to be off.

I have *only* had that when some surface was wet in the car. If a lot of snow is being brought in by the feet, it will help to get non-permeable mats in the footwells. This helps prevent snow-water from being absorbed into the carpet for later release when heat blows out of the lower vents. Before you go on a wild goose chase, find a way to dry out your carpets then use hard mats.

Initially I did not have enough water to pool... only to dampen a towel I started keeping back there. (had to remember to check it before it dried itself out) I initially kept the towels tucked beneath the cubbies in the rear that @Cneu mentioned. I also employed the dehumidification tubs/baggies that he mentioned as well.

You're a very logical poster so there isn't much (if anything) that can be said that you haven't already considered.
It is VERY difficult to know of leaks that would collect beneath the carpet. The only way even begin to see a windshield leak around the top and edges is to pull out the interior pillar covers and roof liner.
In my experiences even with a stripped interior (which is what I ultimately had to do) it can still be unexpectedly difficult to trace a leak. In my special cases, the vehicle had to be driven or parked at a specific angle.

Does the vehicle have a sunroof? Your reply to Sam4 possibly implies a yes?
https://www.fiestastforum.com/threads/water-intrusion-issue-resolved.23553/post-435429
The thread covers multiple sources, not just the sunroof.

If you have stickers that change when directly exposed to water, strategically placing them around the vehicle might help confirm/deny a leak source.

 

[Intuit]

If you have stickers that change when directly exposed to water, strategically placing them around the vehicle might help confirm/deny a leak source.

Apparently there is such thing as "liquid sensor stickers"....
https://www.amazon.com/s?k=liquid+sensor+label+stickers
I don't know whether they respond to humidity (which would be bad) and have no experience with them.