Windows Steam Up

It is true that some of the moisture stays on the evaporator and will vaporize when it warms up. Fortunately it is a much smaller amount of moisture than that removed, so the net effect is positive. The residual moisture should quickly dissipate.

Tom

 

[QUOTE
In my Gen II, I make sure to never use A/C during winter or wet weather, and just keep it on defog at low fan speed. [/QUOTE]

As far as I know for all Toyotas, the A/C come on automatically when the windshield defog setting is chosen. This is true for my III and for my last two Tacomas.

 

many time the glass comes with contamination on them and it cause more fog than if it were clean. mine appeared to have silicon on them,, i had to use something rough like news paper to clean them

usually news papers are just rough enough to cut the crap off.

 

I also have this problem and it way worst than any car I have driven in the past except for old VW bugs.

Does anybody know of a good anti-fog product to use?

TED

 

The fogging on the interior of the windows is associated with the amount of moisture (dew point) in the ambient air inside the car and the inside surface temperature of the windows.

You have to either 1) warm the window (above the inside dew point) and/or 2) lower the dew point inside the car to prevent fogging.

Example - When you put the defroster on you warm the surface of the window above the inside dew point which makes the fog go away. When the defogger is off the window is cooled again, the outside air system closes and the fog returns.

The dew point inside the car - When breathing, people add water vapor to the air. Unless the moisture is reduced the dew point will continue increase causing more condensation/fog.

Reducing the inside dew point - moisture inside the car can be reduced via ventilation with outside air (assuming the outside dew point is lower - which is almost always the case when it’s cold outside) or theoretically via mechanical means - moving air past a cold evaporator/cooling coil. There also desiccant devices but I’ll avoid that discussion here.

I don’t believe that Toyota has established any dehumidification logic relying on the a/c compressor to deal with defogging during cold weather.

But, I have read other comments here on Priuschat suggesting that the system is designed to dehumidify during the winter.

Here’s why - Because operating the a/c compressor in cold weather can cause significant mechanical problems to the a/c, Toyota will not allow the compressor to come on if the outdoor temperature is around 32˚F (0˚C) or lower. Considering this fact, and also considering that dehumidification logic would involve additional sensors and complexity again, I believe that Toyota has no logic whatsoever to maintain humidity control with the a/c operation.

When using the defogger in the Prius the system automatically changes from the “recirculation mode” to “outside air mode”. Once the defogger is shut off the system can/will revert back to recirculation mode, in which case your dew point will increase and the surface of the window will decrease (because it’s not being heated anymore) resulting in the fog, defog, fog condition you've reported.

The best way to eliminate or mitigate the inside window fog is keep the defroster on and/or possible crack a window to lower the inside dew point.

 

Yep, that happened to me over christmas

 

Instead of "Auto", try the "Mode" button: there's a setting that sends air to the footwell and to the windshield.

 

Why is the Prius so much worse than other vehicles? I drove my Dad's GMC Envoy for 50 minutes in cold wet weather with the heater on recirculate the entire time, and never once did the windshield fog and require defogging. This same drive in my Prius would have been the usual battle of defogging every 5-8 minutes. What's the difference??

As a side note, a friend's Mazda 3 is also quite bad for windshield fogging under these conditions. But for some reason, the GMC Envoy is trouble-free.

As another side note, if a small amount of hot engine bay air blew over the front of the windshield, might that solve these issues on the Prius? One could space the hood up a bit or work with the hood seal to allow some frontal hot air flow.

 

I was idly wondering on the same subject: does the car's heating/ventilating system detect high humidity, and react? I don't think so. If you push front defog button preset reactions happen, but that's about it.

 

I think someone already answered that. The windshield is quite large and more slanted in these cars compared to GMC Envoy, combined with the weak air flow from the vents.

 

Even weaker airflow if the ECO mode is on. I would suggest not using ECO until the car interior is warmed through, as it reduces the heater output, including the airflow.

 

Try putting some shaving cream on the inside of the window and wiping it off. I know it works in the bathroom. I've never tried it in the car. Might be a different kind of condensation?

Mike

 

Well what I did on my son's 1972 bug was to give the screen a very good clean and dry it using newspaper as this seems to get the best results. I then used an old trick from my motorcycling days which is to apply a little washing up liquid o a lint free cloth and rub it all over the screen polishing it until it disappears. This generally helps.