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Old 11-27-2015, 11:46 AM   #1
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Question Windshield fogging up while driving in cold weather

We are heading west from Dallas to Las Vegas for the winter. We are trying to get far enough west to get out of the rain and cold temps. Our defroster is running at its max with the temp on hot. We have Zone One heater running with the AuquaHot on gas. I am using a mop to get the fog off the windows in the top corners and wherever else a patch gets started. Anyone else have this problem? Suggestions, short of stopping?

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Old 11-27-2015, 11:54 AM   #2
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It sounds like you have the dash HVAC control set on 'recirculate' which uses inside air over again. That allows humidity to build up and condense on cold surfaces. Especially in the morning setting out we always make sure we have HVAC set to fresh air and even keep the driver's side window cracked open for a bit to exhaust overnight build up of humidity. After a bit the window can be shut because humidity has been reduced. The windshield was probably covered by curtains and got extra cold overnight since most furnace outlets are away from the front of the RV. Open curtains as soon as everyone is decent in the morning to allow air to circulate, perhaps even turn on windshield fans if you have them to help warm them while getting ready to move in the morning.

How many bodies in your RV? (people, dogs, etc) Also, make sure cooking and shower moisture gets vented.


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Old 11-27-2015, 12:08 PM   #3
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True dat! Also, your defrosted should turn on the AC to help dry the air before it gets shot onto the windshield, one side of which is warm and the other side of which is cool. The warm air holds more moisture than the cold air, so when the warm air contacts the cool glass, condensation. The only way to prevent this is to dry the warm air. You can dry the warm air by allowing some cool air in and warming it; the cool air contains far less moisture by the laws of physics.
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Old 11-27-2015, 12:14 PM   #4
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Crack a window while driving on the side that is not raining on or if you have one of those crank out windows, crank it out a little. That will reduce the humidity and the fog should clear up.
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Old 11-27-2015, 12:42 PM   #5
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I thought RV HVAC systems turned on the A/C when you went to heat or defrost modes. Small ceiling fans mounted near the windshield make a big difference.

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Old 11-27-2015, 12:59 PM   #6
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Thank you

Venting the window for just a short time helped. We had three adults and two dogs last night, dropped one adult at the airport this AM. Add in all the cooking yesterday, an extreme day/night of rain in Dallas I'm sure saturated the air inside the coach! Heading into NM on our way to Vegas where the air is dryer so that'll help, too.
Thanks everyone!
Beth and Dave with Hope the Boston Terrier rescue
and her little Boston Terrier boy-toy, Winston
in a 2015 Entegra Cornerstone 45J
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Old 11-27-2015, 01:27 PM   #7
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FWIW a small dehumidifier would be handy if you spend a lot of time in cool climates. That way you can get some of the moisture out when plugged in. That is counter to normal usage so you might get a good deal if you look around. ;-)
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Old 11-27-2015, 05:41 PM   #8
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Are you keeping 1 or more of the roof vents cracked a bit when parked? If not crack them open a bit and this will go a long way to lowering the humidity in the coach, especially when cooking.
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Old 11-27-2015, 07:11 PM   #9
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I have a small computer box fan in the bath vent running 24/7.It helps keep moisture down.
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Old 11-27-2015, 09:31 PM   #10
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It may sound tacky but on those cold mornings with heavy condensate on the windshield I do as others suggested and open the shades as soon as I can to warm the glass. I also carry one of those cheapo box fans and set it up to blow the warm coach air on the windshield and the air movement tends to dry the condensation. The last thing I do is I have a special 12 inch squeegee reserved just for running on the inside to knock down the biggest condensation.
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Old 11-27-2015, 09:52 PM   #11
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Many MH's come with a 12V fan on each side of the windshield. If your's doesn't, they are not an expensive item to buy, found at any truck stop.
MH windshields are such a large area the vehicle's defroster fan will not keep up in cool humid weather while driving at highway speed
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Old 11-28-2015, 07:36 AM   #12
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You are probably there by now if not, drive faster.

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cold weather

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