The other day I was driving along and as it was cold, I had the de-mister on. Once the windows had cleared, I hit the 'Auto' button and fairly quickly, the windows fogged up again. So I hit the window de-mister button again and the windscreen cleared. I have always used the 'Auto' button on all my other cars once the initial mist has cleared because this is quiet and has always worked fine. However I seem to find the windows can fog up when the auto mode is selected.(Its also a bit noisy on de-mist mode) Does anyone else have this problem (PS it was about 7C 40F outside)
Next time this happens, check the air induction button (fresh or recirculation), select the opposite and see if that works better. Although it sounds counter productive, you should try leaving the a/c button on too as it will help dehumidify the air.
We've had similar experience: driving in heavy rain, and set to Auto, it will start to steam up. Hit the front Defog button clears it very fast, but switch front Defog button off and it starts steaming up again, so kind of a viscious cycle. One thing that helps a bit: set it to complete Auto, but then override Mode: one push of mode sets it to Heat/Defog (forces it to split air flow to your feet and the windshield). Sometimes that will be enough to clear the glass, without having to resort to the heavy blast of AC air you get with front Defog.
The A/C button is definitely the answer. Even though you're selecting "Auto" mode, the A/C compressor will not necessarily activate, depending upon inside/outside temperatures. When my interior windows fog, I turn-on the A/C until the humidity normalizes.
That's the remedy that worked for me. However, I live in Los Angeles so the temperatures weren't getting anywhere near as cold as the OP was getting. Those really low temperatures can cause a lot of trouble with the general workings of the car. I thought that the defrost button was really hurting my MPG. Of course, it might have been just the cold weather. I do not know. Mike
sorry to sound negative, but it's a design flaw. windshield is too big or air flow is not set right from the vent, or both. Can rarely get the entire windshield defogged. basically, i have to turn on the main defroster button and keep at least 4 levels of fan going.
One solution is to keep the windshield CLEAN. If it is dirty/greasy, it seems to create condensation points for moisture.
Using any A/C or auto mode at all condenses significant moisture on the A/C evaporator coil, which quickly fogs up the window badly as soon as the A/C stops working. Once you start using it, it becomes a vicious cycle that then forces you to leave the A/C on all the time. 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. Still, the Prius seems to fog up more than other cars.
... and here I thought that "Friar Tuck" had bragged about how he was an "advanced" driver, and knew all there was to know about automobiles.
When moisture condenses on the evaporator coil, it flows to the drain pan below the coil and from there out of the car. The net effect is to remove moisture from the air within the car which is what you need to do to prevent fogging on the inside of windows. There would be a minor rebound effect from re-evaporation of moisture remaining on the coil when the a/c is switched off but my experience has been that this is minor. IMHO, the main reason for having a/c in climates like Vancouver and Victoria is that a/c plus heat is so good at defogging on cool rainy days. I do find that my Prius tends to fog up more than most cars I believe it's partly that the windshield is larger and more horizontal than most and partly because the Prius prioritizes mpg and requires driver action to keep the a/c on. Personally I'd rather be able to see. There are posts in this thread on how to keep the Gen 3 a/c on and I've not noticed a significant mpg hit with my fiddling around, possibly because the Gen 3 a/c is so efficient. The Gen 2 is no doubt a bit different but its hard to imagine that the a/c could not be used to advantage when defogging is needed.
This is a silly comment. The evaporator has a drain which removes condensed water, resulting in less water vapor inside of the car. If that water were not condensed and removed by the drain, it would end up inside the car, causing fogging. Cold weather and moisture are responsible for fogging; it's not the fault of your A/C, unless your drain is plugged. Tom
I've found AC moisture removal (similar borrowing money, meth, and so on) exacts a cost that does cause a moisture dump, when you turn it off. Found this with a variety of cars. I think it's just that all that collected moisture does not make a complete and orderly departure down a drain tube. A goodly amount hangs on the condensor fins: turn the AC off, and it's baaack. It takes an overnight sit before it really dissipates. OTOH, the Prius seems better in this regard.
Hitting "auto" will usually cause the blower fan to direct air to the floor. I would suspect that most humidity / moisture would be on the floor where your wet boots sit on the carpet. Try using the windshield defogger setting. And there is a difference between defogger and defroster. You're Welcome
