Why does the windshield windscreen fog up so much?

tivoboy · 12-05-2008, 12:04 PM

So, this seems to be getting worse as the weather gets a BIT colder, but it has been an issue for months now.

Get in the car, start driving, windshield fogs up. I have to switch the center control to the 12 oclock position (which essentially is the defog and AC on) and it goes away, but of course I cannot keep the heat on, and I have to switch it back and forth.

Is there something here, is there a coating one could put on it? Does it go away if the heat is higher in the cabin (this has not been my experience, my experience is it just STAYS this way)

btw, I did a search

rawlusÂ® · 12-05-2008, 12:14 PM

the 12 o'clock position activates the A/C compressor which dehumidifies the windscreen - heat has only a little to do with it. if it's too hot, you can lower the temp with the slider and still benefit from the dehumidifying effect.

i suspect that the relatively small cabin size combined with the moisture you breathe into the cabin along with any evaporation of water from floormats or elsewhere as is common in winter along with relatively dry air when it's cold all contributes to accelerated condensation on the inside of the windscreen in cold weather.

there are coatings like Fog-X from the makers of Rain-X but i don't personally recommend them. their efficacy is short-lived, they are often a PITA to apply and they can introduce their own issues like streaking and blurred vision.

lastly - in some cases i've noted that if the A/C drain is blocked or obsctructed enough to allow moisture build-up within the vent system - sometimes merely turning on the vent or defroster can have an immediate effect of blowing moist air onto the cold windscreen and this can cause instant fogging with will then have to be overcome by the A/C's dehumidifying function after a few minutes of run time. so if you notice the fogging being extremely pervasive and linked in some way to your activation of the defroster - have a service tech check out the entire HVAC system for any standing water, excessive moisture in the lines, etc.

also - recirculate will sometimes accelerate the dissipation of the fog on the windscreen when used over short periods under the theory that you are continually projecting drier and drier cabin air across the windscreen. once it clears you can then turn off the recirc function and run normally.

John_H · 12-05-2008, 12:23 PM

Here's a suggestion:

Clean the inside of the windows.

I've been lazy cleaning my own and I've noticed the fogging being a little easier to happen. I know that if I clean things well, the improvements will be extreme - it just hasn't been bad enough for me to spend the 10 minutes with it. I can see the difference in the edges where I didn't clean completely the time before.

**rfernatt** · 12-05-2008, 01:01 PM

Quote:

Originally Posted by tivoboy

So, this seems to be getting worse as the weather gets a BIT colder, but it has been an issue for months now.

I hadn't really noticed the effect until the weather turned colder. Now, in the mornings with two passengers and two cups of hot coffee, it does start to fog up the windshield. Actually, I've had the fog turn to ice on the inside bottom of the windshield.

I usually just set the vent control at about 2 o'clock where it is a smidgen on the windshield and blowing the rest out the front vents and that takes care of it without using the A/C compressor. Unfortunately, your feet might get cold, so you may have to vary some. I'm at about 5 - 6 o-clock for a while and then switch to 2 o'clock after things are warmed up and the windshield starts to look hazy, but I have about a 50 minute commute.

John_H · 12-05-2008, 01:06 PM

Quote:

Originally Posted by rfernatt

I'm at about 5 - 6 o-clock for a while and then switch to 2 o'clock after things are warmed up and the windshield starts to look hazy, but I have about a 50 minute commute.

I'd like to take my commute from about 5 - 6 o-clock and switch to 2 o'clock. Traffic is much lighter. Trouble is I'd have to get up at 3am to do work that out with my boss.

mendo · 12-05-2008, 01:13 PM

I got a small chamois for cleaning the windshield, it works really well and doesn't fog up for a long time.

CRC2362 · 12-05-2008, 01:17 PM

Make sure your Recirc button is not on

**rfernatt** · 12-05-2008, 01:22 PM

Quote:

Originally Posted by John_H

I'd like to take my commute from about 5 - 6 o-clock and switch to 2 o'clock. Traffic is much lighter. Trouble is I'd have to get up at 3am to do work that out with my boss.

Uhhh... That's 5 o'clock and 2 o'clock on the ventilation control dial!

Unless I'm overlooking the humor...

There is absolutely no traffic where I live unless deer count! One stop sign on the way to work and two stop lights and four stop signs on the way home from work.