Deano

I've got frost on the INSIDE of the rear windshield! Wud up wid dat?

Today was a very cold and windy day, 23 degrees and with wind chills into the single digits. I took a ride a lunch time and the sun was out. The frost was there after work during my ride home. Where's the moisture coming from? Is this normal? The rear defrost didn't do a very good job of clearing it. I really don't like the idea of having to scrape the inside of the window.

Is this a common issue? Is there something the dealer can fix?

nickolas_g

It is simple physics. If there was enough moisture on the inside of your car it is possible.

boukehj

Whatever you do, don't scrape the inside of windows with scraper!!! Use a cloth or something. It will result in scratches. Basically, only the outside of the scraper makes contact with the window and before you know it...
I've had this happen on the front window of my other car. I constantly have to look at faint scratches...
Being the rear window, also be careful that you don't damage the rear window heating lines.


About the moisture itself: it can be anything. Normally, the airco would take out most of the excess moisture. Of course this requires the airco to have a good way of getting rid of the moisture; sometimes the pipe that sheds the water gets clogged (own experience, but with other cars).
But there are 100 other ways how moisture may build up in a car. You may want to check that the floor mats are dry.

narvselius

You can also invite a couple of friends in the back seat and give them plenty of vodka. That will also reduce the frost.

Seriously, I would recommend that you buy BMW's de-ice product. I never scrape my windows knowadays. Just spray... wait... ok, wait a bit longer if it's really cold and then wipe off!

BMDiesel

If you don't drive the car long enough to dry out it becomes visible when frost comes around.

If no frost, then the climate control will remove the moist quickly so you won't be bothered by it.

After a stop (with airco on before you stopped) you sometimes notice moist on the front window inside, that's because the airco first sends a blast of humid air (because of the cold condensor being wet due to condensation) and then dry air as the condensor starts to work properly.

So the way to avoid this is by reducing the use of the airco when you don't really need it anyway: especially around 5 degrees centigrade. Leaving it off also reduces the build up of fungus in the ducts though that is mostly a summer problem (moist ducts heat up/moist up/cool down/heat up/moist up/cool down and growth starts)

However, when you want to get into the rythm of non-airco unless you-really-need-it rather than always on follow this procedure:
You'll need to do quite a long trip. Start off with airco on; the warm and dried air must flow trhough the car for a long time to even out everything and have all wet spots dried up (easier to do this in fall as at temps below 5 C the airco won't work anyway). Then when it's really really dry everywhere it's time to turn airco off to dry out the ducts. Do this at the very least 10 minutes before you stop the car and in the above procedure, something like 20 minutes or more remaining driving time. This to dry out the ducts and the condensor to warm up to outside temperature so condensation will not occur at standstill.

ExGMan

Another thing you might check is to make sure that the air recirculation control is set to remove the air from the car interior. I believe it's the lowest (of three) buttons to the right of the passenger temperature control knob. If you have a green LED lit there, it should not be to the left of the arrows-in-a-circle symbol. Check p. 91 of your manual.

I spent a lot of time out in the rainy & wet weather this past Sunday down in Rhode Island. Every time I got into the car, I know I brought a lot more water which became water vapor in with me. I didn't have any issue with fogging, and didn't have to run the AC at all.

Heelsonwheels

Whatever you do don't scrape the inside of the rear backlight(window)!!...use the rear defroster and play with the climate control including using the AC function to dehumidify the car. I didn't feel the heat on my feet was warm enough and didn't know why.....Just yesterday I saw how to adjust the air temp throught the idrive. Also make sure the cowl and trunk are clear of accumulated snow and ice.

BMDiesel

Oh yes, indeed, air intake and exit should be free of anything blocking. Such as leaves and snow. I'm not sure how/where these things are but in my previous car this was under some covering but did accumulate a pile of leaves thus blocking fresh air intake.

I often open a rear window a little bit and put the fan higher when I need more performance (clearing the air)