Why do my Windows Fog up so Much???

Not using the fans is probably your problem. The windows are fogging up because there is a temperature differential between the outer and inner glass. Venting in outside air will help.

Also, keep the inside surfaces clean.

 

I'll rephrase your question: why is the humidity high enough, and heat inside the car low enough to fog up the windows ?

If you know the outside humidity and heat, your inside cabin temperature, and think about anything people in the car are doing to add water to the air, your answer may be answered. E.g., a new habit of taking hot coffee into the car would do it.

Short answer: crack a window.

Sort of short answer: Some people ignore the physics and just apply rainX to the inside window. I gather one possible downside to this approach is an increase in glare in certain situations.

 

Um. Two possibilities:

1. It really is that humid out.
2. You've got the AC button turned off.

The Prius, with the environmental controls set to Auto, will cycle the AC on and off when it thinks it should, and that includes when it's cold or humid out. But it will only do that if the AC button is lit.

I'll say that it works, kind of, although I've found that in the right kind of snowstorm the car will sometimes have to be put into defrost manually in order to clear the windows.

But if the AC button is off the windows will fog up lots more often. Leave it on.

KBeck

 

maybe the vegetable plastics give off more humidity than civics.

 

To some extent AC use is addictive, since it leaves moisture on the evaporator coil that gets airborne when you use the system next.
Don't be stingy with the blower fan. In the big picture (blower fan vs. vehicle traction motor use) its effect is miniscule. After it stops raining (and it *has* been raining lately) make it a point to put it on windshield/floor setting and bump the fan speed up to 3 or 4 bars for a while to allow things to dry out.

 

Back in the day I owned a Datsun B210. Lousy car, decent gas mileage, bought it used, it had had a blown engine and wasn't put together Quite Right, etc. The original buyer got it without A/C. But, geez, put the fan on high and the blame thing would blow you into the back seat, so even 100 F days wouldn't make you too hot.

I've had a Civic. Its blower isn't in the same class as that B210, but it's definitely better than what the Prius has. Better air circulation plus the fact that the auto mode in the Prius tends to turn the fan speed 'way down means that the Civic's windows stay clearer.

Like I said: keep the A/C button on.

KBeck

 

By the way, cracking open one window will not let much air circulate. Best are two windows, diagonal from each other.

Just mulling over possible differences between a Prius and a Civic, I wonder if the front window of the Prius is more sloped and that makes it easier for water to condense there.

 

The climate control has buttons which let you choose between outside air and inside air (recirculating). This operates even when the fan is off.

My guess is that you have it on recirculating. Tap the button for outside air, and keep it there. That should clear up your condensation problem.

 

Use the ventilation blower. Even if you ran it on high all the time, it would not drop your fuel economy by 1/10 mpg. Even using the Defrost setting where the AC runs a bit to dehumidify the air, uses very little power.
Keep the windows clear and be safe.

 

That's the ticket. "Rebound" has it correct.

 

Here in Vermont, I have to run the HVAC in windshield/floor setting most of the time for most of the winter. I'm no stranger to managing windshield fogging, but there is just so much glass and with our particular climate, I'm having to get air onto the windshield frequently. I also never (quite literally never) run the air in recir, it's always bringing in fresh air.

The thing I don't like about this is that, no matter what, if a Defrost setting is chosen the AC compressor WILL run. And that does hurt efficiency (though it's good for defogging, obviously). Pretty much every modern car works this way, the AC is coupled to defrost settings to dehumidify.

I wish I could just run fresh air to the defrost vents, I think it would do the trick 9 times out of 10.

 

I have this problem too, but have found a solution. Prius is a chick-magnetic and having all of those hot, steamy bodies in your car causes the windows to fog. Locking all doors quickly, before they get into your Prius, should prevent this nuisance.

 

The button next to the Fresh/Recirculating button lets you direct airflow to the windshield; it has a Defrost icon. Using this will not engage the AC, and it will remain in effect even even the fan is off. The two other Defrost buttons control Front and Rear defrost. Only the Front button will engage the AC.

 

The MODE button? Sorry, but you are mistaken, if you choose the feet/defrost position there the AC compressor WILL cycle on. The Big Defrost button on the far passenger's side below the fan speed buttons will as well.

If you choose face only, feet only, or face/feet the AC compressor won't come on unless you hit the AC button.

I've played with this extensively for over 2 years. If there is a Defrost icon lit (either in the Mode window of the big Defrost button) then I've found no way to keep the AC compressor from running.

At least that is how it is in my 2010.

More discussion: Does A/C automatically run in defrost mode? | PriusChat

 

I don't know how it is in Civic but certainly this is one of the main reasons.

 

The only setting for no AC or heat is LO, with the mode set to something not directly involving the windshield. Any temperature set above that has the potential to cause the engine to run when it otherwise wouldn't before it's warmed up. The exception to this is FAN OFF but unless you're moving enough to force air thru the stationary fan it's effectively "system off". Of course if you're driving above 30 mph or so things will be warmed up enough within a mile anyway.
It's really dependent on what's needed to keep windows clear for safety and on your personal comfort level.
I dress warmly enough to have the temperature set to LO with the mode on windshield and floor for my first 3 miles at just about any temperature above 15 degrees. But I'm unusual.
Don't be crazy--just experiment with your options from day to day. It'll be a moot point in another week or two even up here in the Great Lakes. Spring is coming soon.