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Old 08-07-2012, 03:34 PM   #1
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Question Outside Air Intake

I have a 2001 Cherokee Sport with which I am having a problem. Which is, that even though all the heat and A/C systems are working fine, my front window still fogs up when it gets cool outside. Have tried running the defrost with both warm and cold air, with and without running the fan (and yes it is blowing plenty of air on the windshield) and while the cold air helps a bit, it makes for some uncomfortable driving conditions particularly for the wife. Thus I am sure that somewhere along the line the outside air vent has become clogged, detached, etc. Or at least that;s my best guess. Has anyone else ever had this problem, and if so what's the solution? To include, will I really have to take the entire dash off to get to the problem? Thanks very much for any help you can pass along.
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Old 08-07-2012, 03:47 PM   #2
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I don't understand what you think the problem is... If there's plenty air blowing on the windshield then what makes you think the issue is with the HVAC system?

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Old 08-07-2012, 03:56 PM   #3
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Is the fog on the outside maybe? lol
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Old 08-07-2012, 04:02 PM   #4
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When using your defroster, is your ac pump kicking in? Im not sure exactly how it works but there is a dryer of sorts that takes the moisture out of the air. I would check that first.
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Old 08-07-2012, 04:04 PM   #5
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Try the heat defroster. That always does it for me!
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Old 08-07-2012, 04:43 PM   #6
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Defrost without the fan? Unless you installed a switch to bypass that the fan is on as soon as you select a mode on the center ****

Also I've had this happen on super humid days. Sunday it rained pretty heavy here - had to run the defog up front to clear the condensation from my breath. Trouble is since the AC compressor engaged it cooled off the glass which caused condensation on the outside - had to keep the wipers going lol.

In the winter I used that Rain-X stuff that lowrange2 posted. Very happy with it, but don't try cleaning afterwards lol
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Old 08-08-2012, 01:41 PM   #7
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Default Outside Air Intake

Thanks to everyone for replying to my initial post, but not sure anything fits the bill so to speak. The moisture forms on the inside of the window, and turning on the defrost with the heat on doesn't solve the problem. In fact it gets worse. Turning the heat completely off and running the defrost fan while at the same time rolling down the windows helps some, but makes it uncomfortable to drive, especially for my wife. Is the A/C pump kicking on? Don't think so but I will check.

Again, my thought is that what is happening is that somehow the outside air flow that balances out the humidity in the vehicle has been cut off. Say this because I used to have a Ford Taurus which had a cabin filter that filtered the outside air, and about once a year I had to replace it because it would become dirty and cut the air flow off.

Again, thanks for the replies.
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Old 08-08-2012, 02:46 PM   #8
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If your AC works, then yes. The spec (at least for newer XJs) is to engage the compressor when defrost is selected and the temp is over freezing.

Unfortunately no cabin air filter in these beasts
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Old 08-08-2012, 04:32 PM   #9
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Try selecting one or the other "white" vent selector positions that are not circled in yellow and adjusting the temp selector toward the "red" portion. The 2 "white" non-circled positions are the only 2 positions that do not engage the a/c compressor. All of the vent selector positions circled in yellow engage the a/c compressor regardless of where the temp selector is set.
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Old 08-08-2012, 04:48 PM   #10
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Crack a window n call it a day
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Old 08-08-2012, 07:26 PM   #11
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djb383, is that button highlighted in a red circle for bypassing the compressor? I've been fancying installing one so I can run all those options without wasting even more gas lol
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Old 08-08-2012, 08:20 PM   #12
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Quote:
Originally Posted by salad View Post
djb383, is that button highlighted in a red circle for bypassing the compressor? I've been fancying installing one so I can run all those options without wasting even more gas lol
Negative on bypassing the compressor. That pic is from one of my very 1st posts here asking if that switch (red circle) was factory or not. Our XJ is a plain Jane SE model and that switch (and door/hatch lock servos) were installed by the PO so that the 4 doors and rear hatch could be locked/unlocked with that dash switch. Far from remote keyless entry but at the same time, handy as a pocket on a shirt for a 5 door vehicle.
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Old 08-09-2012, 12:39 PM   #13
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DJ, Salad...thanks for the additional info. Unfortunately I have just tried setting the heater to the non defrost settings, which is another reason I feel its not getting any outside air. Not sure about running the A/C but will give it a try. But dang, hate to cut the mileage even more. And, lol, not sure who said to just open a window...but even that doesn't work!!! I guess I'll either keep trying a combination of things, or give in and pull the dash to see if the venting system is clogged, colapsed, or whatever the situation might be. Have a good weekend guys.
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Old 08-09-2012, 01:03 PM   #14
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if it really is condensation then opening the window would clear the windshield over time. Are you sure its condensation and not a bad heater core blowing antifreeze on the WS?
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Old 08-09-2012, 01:31 PM   #15
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I would suspect either a failing heater core blowing water vapor through the system, or a clogged condensation drain. Do you ever get in your Jeep and smell a maple syrup smell? If so, you probably have a failing heater core. Not good.

To the OP, the way an automotive defroster works is, in part, by dehumidifying the air, not just blowing it around. In addition the airflow over the glass, either hot or cold, the primary way the system deals with the moisture is to have the air pass over the AC evaporator coils first. This is why on most vehicles, the AC compressor is designed to kick on in the defrost settings. This allows the coils to get cold, and the moisture in the air passing over the coils sticks to the coils and freezes, thus dehumidifying the air. When the compressor cycles off and the coils warm up, the condensed ice melts to water and drips into the bottom of the chamber and is routed out through the condensate drain that goes through the firewall. If you raise the hood and look down from the passenger side, you can see the small black plastic drain tube sticking out of the bottom of the firewall, down below the dryer/accumulator.

The other reason that the compressor is designed to kick on is that in some situations during the cold/cooler times of the year, the AC system may not be needed for months on end. Sitting this long without use can cause seals to dry up and/or harden, which could lead to system failure or leaks. Having the compressor kick on even periodically during the winter months (when you are likely to use a defroster) helps keeps everything in the system lubed up and functional.

I would run the defroster or AC on a humid day for 10 or 15 minutes and make sure you see water coming our of the condensate drain. Have the system set on a non-recirculate setting, and also some mid temp setting, not full cold, so that you can be sure the compressor is occasionally cycling off and allowing the ice to melt. If you never see any water draining, you probably have a clogged drain, thus the water never goes away. You can shove a screwdriver in the drain to make sure it open, You won't hurt anything.
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