Need defrost running all the time?

AC needs to be on ... I never have mine off --

 

I agree with Tideland's post - you need the a/c to dry the air - there's a defog button too.

But have a read of the Owner's Manual - it almost always turns the A/C on too, but I've noticed a couple of times I had to do that manually: The manual omits mentioning turning ON the A/C - probably because it expects it to automatically do so.

 

I leave mine on "Auto" and let the system decide whether or not to put the A/C on. I notice it changes when I put on the windshield defogger is on. I let the system do its thing with the minimal of interference from me, and I am satisfied with how it performs.

 

Try weaning yourself from AC. It is tough when you've run it a while and then turn off: you'll get a humidity dump. Try turning up temp a bit and rolling the front windows an inch or so. After about 5 minutes the humidity will clear.

I wish the car would allow you to direct all air to the windshield, without AC, that would help.

 

Do you have any wet objects / cargo / floormats / waste storing moisture inside the car? Or any rainwater leaks?

When you turn the defrost off, are you going into a Recirculate mode that retains your respiratory moisture inside the car?

 

I lived in the tropics, and, in lowlands areas where it didn't get cold in winter, but the humidity was high all the time. I would guess that the A/C was on almost all day and most of the night. A/C dried the air even if directed to our faces, but at a hint of fog on the screen, I'd redirect it to the screen again till it peeled off.

Outside air (not recirc) will almost always be dryer than inside air, A/C air will always be dryer than non-A/C. I'm not sure what the DEFOG button does on PRIUS - but I'd suggest experimenting with it in conjunction with the suggestions above.

 

In mine it's labelled Front and it puts the fan to max up the screen. I used it this morning (+2°C) but the AC was already on. Therefore can't say for sure if it would bring AC on automatically. Humidity was high enough here for considerable amount of dew to be on the car at first use.

 

I learned this, try hitting the auto button (if not already on) and not using the defrost button and change your output to windshield/floor vents. This works well for me in florida to avoid the car starting and running till the car warms up. You can change the fan speed after doing this and the car shouldn't start right away unless the outside temperature is cooler than the inside demanded temperature or it is less than 32 degrees Fahrenheit.

 

Hi Tissimo, I live in Oakland. With all the rain and cold weather we've had my new car is damp inside. I'm using the defroster often. In my experience, if I use either the defrost button or toggle through the heater settings to defrost/foot my windshield clears up right away. I don't have to turn on either AC or auto.

But I can't get the controls to let me turn on defrost and recirculate air strikes the same time. This is an issue for me because I'd like to be able to shut out bad smells and keep the defroster on. I'm driving a 2016 Prius 3 today (dealer loaner) and the recirc button works with the defroster. I'm wondering if it's something in settings.. I will go thru the manual again tonight.

 

Just to muddy the waters:

With AC off (button not lit), and mode set to Heat/Defog, our car will run AC occasionally, a sort-of "stealth AC mode". It seems to depend on ambient temp, and maybe humidity? Not sure: is the car detecting the latter. With a ScanGaugeII hooked up and monitoring AC compressor watts, it would show values other than zero in Heat/Defog, sometimes.

 

If you are breathing, you are producing the moisture fogging up the windows. If your car is parked outside, then the temperature delta between your face and the interior of your car is enough to cause steam.

Since you are local, I can at least corroborate your story. Ditto in the east bay. Defrost has to be on all the time. I use the feet and windshield setting on low and it is sufficient to maintain the windows after initial clear. This isn't specific to the Prius though. I've had to do this in all my cars.

 

True that. The windshield can be on the cusp of fogging, and I start thinking: better not talk too much, breath through nose, lol.

Cars used to rarely have AC, we got by. It takes a bit of window roll down, just an inch or so. If it's raining hard, just barely cracked. Plus keep the temp setting highish, fan going moderately, as much as possible directed at the windshield. Which with the Prius' modes (sans AC) is sadly only 50/50, the heat/defog mode.

The above works for me, most of the time. Some rainy nights, safety trumps: I throw in the towel and use AC.