Prius Misting Problem

[SimHo]

I've had my gen 3 prius for about a month now, and am a very happy camper indeed! The weather has been good since I got the car, but now that the temperatures are beginning to drop, I'm finding that I am continually having to push the demist button to keep the windscreen clear. I thought the climate control was supposed to keep things under control - it does in other cars I've had with this feature. Just thought I'd ask if anyone else has noticed this, or whether I have a problem. Thanks in advance!

[Joseph D]

I've had my gen 3 prius for about a month now, and am a very happy camper indeed! The weather has been good since I got the car, but now that the temperatures are beginning to drop, I'm finding that I am continually having to push the demist button to keep the windscreen clear. I thought the climate control was supposed to keep things under control - it does in other cars I've had with this feature. Just thought I'd ask if anyone else has noticed this, or whether I have a problem. Thanks in advance!

I don't know what the science behind it is, but it seems that in the colder weather (about 5 C and less, I guess) you get better results if you do not recirculate the air, that is, you need to draw in fresh air. Also make sure the A/C is on as it helps dry out the air.

HTH.

[Bibsy]

If you haven't changed your cabin filter, and don't know when it was last changed, get one for a few pounds from the internet or your dealer's parts department and change it yourself (or spring for the dealer to do it if you're feeling flush).

[cuius]

Think it's a Toyota "feature" - had the same problem with the Auris HSD mk 1 following an early morning start last week.

[johalareewi]

Seems to be a common problem with the prius gen3 at least.

Topic comes up regularly.

Just use screen demist mode and keep windows clean.

[Grumpy Cabbie]

Make use of the climate control. Leave it on Auto at about 20/22 depending on preference and leave the a/c switched ON.

The Auto function will only use a/c if and when needed and will help keep your windows fog free. The a/c doesn't use much more fuel in summer and is barely on otherwise, in that the car uses it only when needed when using Auto and makes no dent in mpg's.

Using a/c does go contrary to what some think in that it should only be used on very hot days. Seriously, leave the car on auto with the a/c on and 9/10 times it'll keep the inside dry and clear. The only time it will struggle is in the first 2 miles on a cold morning where you should use the windscreen defrost setting. There should also be no reason to use the rear demister.

Follow this and you'll have clear windows all year round.

(I read you have a 2011 car. There is an issue with BRAND NEW hybrids where they do mist up for the first 2-3 weeks. This is normal and will clear eventually)

[SimHo]

Thanks for your responses. I do have the climate control on all the time - set at 21c or so. The problem seems to happen once everything is warmed up and putting the A/C into demist mode actually makes things worse. However, the front screen demist button just under the fan speed buttons clears the screen in no time, but it seems a bit off that I have to do that manually when the car is supposed to be doing it for itself! Does anyone think that this could be caused by a blocked cabin filter?

[Grumpy Cabbie]

Do you use AUTO with a/c ON?

Do you have the recirc setting on or do you use air from outside?

If you do and you do more than 2 miles, then you probably have a leak or a blocked a/c drain. If you don't use a/c with Auto all the time, then there's your problem. Check all your windows are up, even if they look up. Give them another little tug of the window switch as they can drop 1/4 inch. Also check the rear boot seals.

But I really would be curious to know if you leave the climate system on Auto with a/c all the time. Switching a/c on manually when you think it's needed will have allowed too much moisture to build up in your car (inside the seats, behind the dash etc).

[SimHo]

Hmmm...thanks Grumpy cabbie - I'll keep careful watch on the settings for the next few days and report back. I normally use the "outside air" - the auto switch is certainly on, but I'll make sure a/c is on too - can't swear to that, but I'm pretty sure I would have picked that up because I do like a cooling breeze! Thanks for your input. I'm going to bring the problem up with the supplying dealer later, we'll see what they have to say about it.

[Grumpy Cabbie]

Hmmm...thanks Grumpy cabbie - I'll keep careful watch on the settings for the next few days and report back. I normally use the "outside air" - the auto switch is certainly on, but I'll make sure a/c is on too - can't swear to that, but I'm pretty sure I would have picked that up because I do like a cooling breeze! Thanks for your input. I'm going to bring the problem up with the supplying dealer later, we'll see what they have to say about it.

The a/c light might be lit but when you use the Auto function the a/c is only actually switched on internally when needed so you won't get a cooling breeze in winter. Firstly you will have the heat on to keep you warm and secondly the a/c is also used to dry the air and the car has a built in moisture sensor. That way if the car starts to mist up the car uses the a/c ever so slightly to dry the air, switching it off when not needed; hence Auto setting :)

So you get a nice warm, dry and non misted up car. There is no cooling breeze. Told you it's counter intuitive, as are many things about the Prius.

Or maybe your a/c gas needs topping up?

[cuius]

After further experiments with the Auris systems found it's better to use the front demister button for an initial clearance (i.e., full fan, a/c on), but after that, because the a/c tends to chill the windscreen and thus increase the condensation, just use the "mode" switch to direct warm air upwards. Additional advantage is that this is quieter than demister mode.

[SimHo]

Grumpycabbie, you are a genius!

My problem was almost certainly that I assumed the a/c was fully on when the Auto button was depressed. On checking the car, I realise that the a/c was in fact off.

Hopefully this will solve the problem.

Thanks again

[Grumpy Cabbie]

It should, but as I and others have said, first thing in the morning and for the first couple miles use the Windscreen Demister setting until the car has warmed up.

p.s. It's a common question on the US forum and 9.5/10 times it's that people have switched a/c off or have the car set to recirc and thus restricting full air flow from outside. I knew it wasn't the car as taxis mist up very quickly when you have 4 passengers on a rainy day and the Prius on Auto setting (with the a/c on B)) could easily keep the car from misting up.

Glad all sorted.

[IanIanIanIan]

Consider the aircon button and light as 'A/C Enabled' not on, i.e. ready for use when the car decides to use it depending on the other climate settings selected.