Windshield fogging... MUST have on AC

[giggles]

Hey y'allI just thought i'd throw this out there... I've noticed that if I dont have my A/C on (particularly in the morning this time of year) my windshield fogs up super fast. I click it back on and the fog goes away almost immediately. Just wondering if anyone else has noticed that their windshield gets foggy really quick if they don't use the A/C?

Not particularly upset; just curious...

[Rockhound]

Well, it all depends upon weather conditions and how the temperature inside your car compares to the temperature outside. I'm guessing that the humidity is pretty high in your area, too, which makes the incoming air behave similar to breathing on a cold windowpane. Just make sure your climate control is set to intake outside air and leave the A/C on. You can run the A/C on whatever temperature you like without any problems - you can run it full hot in the winter time with the A/C on, just to dehumidify the air.

That said, I have noticed some cars fog worse than others. My first car (93 Sentra) fogged up like crazy, but my current car rarely does so (G20). I also haven't encountered any fogging in the Versa yet, although weather conditions haven't been conducive around here just yet. I'm not sure why one car would fog worse than another, other than perhaps the design of air intake ducts and how much they are affected by the heat of the engine and such.

[Guat]

I have been noticing the same problem the last few weeks in Toronto. I do put the AC on and it fixes the fogging. I also find that leaving the windows open a crack helps.

[matt_a]

You might also want to check and make sure you have the airflow selector set to bring fresh air in from outside and not Recirculate. I've noticed before that if I leave it on rec, the windows will fog very quickly.

[bikeman]

You might also want to check and make sure you have the airflow selector set to bring fresh air in from outside and not Recirculate. I've noticed before that if I leave it on rec, the windows will fog very quickly.

This is certainly true but I've always wondered why it's true. Bringing in outside air when it's raining cats & dogs has a relative humidity at or just below 100%. The air inside has to have a lower RH. Why does the outside air produce better results in all conditions?

David

[Rockhound]

This is certainly true but I've always wondered why it's true. Bringing in outside air when it's raining cats & dogs has a relative humidity at or just below 100%. The air inside has to have a lower RH. Why does the outside air produce better results in all conditions?

David

I've always thought that it fogs so bad when it's on Recirc because of the driver's/passengers' body heat and the humidity from your breath. The cabin of a car is a pretty small space, and when it's entirely sealed up, the air gets stale pretty fast.

But you're right about the relative humidity during rainfall - and that is odd that is still performs better on "fresh air" than recirculate during those conditions. It must have to do with the efficiency with which the air conditioner dehumidifies the outside air that is relatively 'forced' into the system versus how it handles recirculation.

[matt_a]

Yeah...I like Rockhound's answer. Let's go with that.

[matttail]

the car is more likely to fog when you're recirculating air because you're not blowing air on the windshield or windows. that means a greater temp difference and causes condensation. When you're recirculating air it's drawing from the windshield vents to blow somewhere else. Aside from that you're body is made up of 80% water, so when you exhale it's moist. (and I assume you're not trying to recirculate air while blowing on the sindshied - cause that doesn't get you anywhere and is a no-no for the health of your blower motor.)

When things are equal on both sides of the window - bring in outside air during a rainstorm, there is more of an equilibrium between sides of the glass - and thereby less chance of condensation.

Take a glass drinking cup outside during a rain storm - it may get wet on one or both sides of the glass - but no fog will form. Now fill that glass with ice water and see what happens. The exact same principles apply to your car. The glass is a little thicker, so reactions are slower - but it's the same ideas.

[bikeman]

(and I assume you're not trying to recirculate air while blowing on the sindshied - cause that doesn't get you anywhere and is a no-no for the health of your blower motor.)

Why are you assuming this? Why is it a "no-no.?"

David

[Ever Victorious]

One thing for sure is that newer cars are far more well sealed than older cars, so what moisture IS in the car stays there for much longer.

I find that cracking a window a little helps, but if it's raining I just give up and run it with the A/C on. A/C works even in heated modes, it dehumidifies the air all the same.

[CodeRed]

Rain-x makes a anti fog product....That i need to invest in.

[matttail]

Why are you assuming this? Why is it a "no-no.?"

David

I assume this is a no-no because the vent selector in my car has an X over the circulate icon. I think the manual says something about that too.

As for the Rain X anti-fog my parents got some, and had a horrible experience with it. I don't know for sure if they didn't put it on right or not, but it smeared all inside and they had all heck getting it cleaned back off - so make sure and test it on a corner of the windshield first.

[giggles]

Thanks guys, good to know there's other people out there who've noticed this. Just to be clear, I almost always have the vent set to bring in outside air. The only time I don't is when I'm stuck behind a big smelly truck in afternoon traffic. And you right, it does fog more then. I'll keep the A/C on for the forseeable future... I'm in the Northwest. We said good-bye to the sun about 2 weeks ago; she should be back sometime around March or April

[GiLLT]

giggles i have the same problem as you, cracking my windows usually helps for a bit, but i usually just throw the AC on real quick goes away quick and then i just turn it back off till it fogs again, its rather irritating but atleast it works. ive had this problem with my versa since i got it almost a year ago this month. ive never had this fogging problem in previous cars its kind of weird, i ask people around here if this ever happens to them and they say no. but whatever its the little things that bug me when they shouldnt. i have no real complaints. i think i will try that rain-x stuff, it cant be any worse than armorall wipes, those smear worse than anything and when your car fogs after using them, good luck getting it unfogged.