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Windows Icing up while driving

I have a 2002 Dodge Ram Van 1500 (conversion), in the winter on long drives on a cold day. My side windows fog up then ice over. I have to run my defroster on high fan just to keep the windshield clear. However if I stop (like at a shopping center) and let the engine idle. The windows will clear up, even if they are iced over. This has happened over the past couple of years. During the summer the A/C works just great. In fact, my wife will tell me to ‘shut it down’ because she gets too cold. I cannot hear any window leaks, but cannot rule that out.

Are you operating the HVAC system in the “fresh air” mode? If the system is in “recycle” it will hold moist air in the vehicle and the windows will fog. Setting the system to “fresh air” should help dry the air and defog the windows.

It’s also possible there’s a leak somewhere, and moisture is getting into the vehicle when it rains or snows.

There is no option for “fresh air” mode. Knob from left to right

Off, Max A/C, A/C, vent, vent/floor, floor, def/floor, def

How can I test for leaks?

Coolant loss will be the first indicator of a leak. As an option you can try opening the rear windwos a bit to let the humidity escape.

Is the engine getting up to full operating temperature?

If it is, and you have no operational problems, my only thought is that the system is too small to remove the moisture of that large a volume of air. Perhaps even the heater is insufficent for that volume of air in your driving environment. That’s a lotta air. That’s a big vehicle.

The only other thing I can guess is that the defroster vent doors inside the ductwork are inoperative. Does air blow out the vents when you put it on defrost?

Are you the original owner? Has it always done this? How cold does it get where you live?

I looked at some pics on ebay and saw no indication of a fresh vs recycled air control. Kick the snow off your boots, and use the defrost mode as that removes moisture from incomong air, and rear windows open. As I saw no control for fresh vs recycled air it is possible the drain line for the ac is plugged. An easy fix with air pressure ala click and clack. Search it, or if you have trouble I will try to look it up.

The Max setting recirculates the air and the A/c setting takes in outside air.put on a/c and turn up the temp,the a/c compressor will remove the moisture from the air. The defrost setting should also operate the a/c.

yes, as stated this usually happens on longer drives (:30min-5hrs)

also - if I stop (like at my destination) and let the engine idle. All windows will clear up in a couple of minutes. No frost, No fog

In my wee little vehicle, the “fresh air” control is a separate button near the knob. I think it would have to be, b/c vent, vent/floor, etc. are independent of whether you want fresh air. There are probably a dozen different names and signals for this setting. I think mine has a circular arrow.

My little egg-beater also automatically sets it to fresh air every time I switch it to defrost.

BTW, I drive a little car, b/c they warm up faster in the winter ? a lot faster.

Idling my engine causes sharp pains in my wallet. I can literally feel the pain.