1. #1
    Join Date
    Sep 2013
    Posts
    99

    Problem w/ intermittent defrost a/c

    Have a '11 Crown Vic with 290k miles and I've been having a problem with the windows fogging up all the way around. The defrost seems to be working about half the time. On humid rainy days it'll work for say a half hour keeping the windows clear, then the windows will fog hard for 10-15 mins. And then it might decide to start working again, back and forth it goes. When I started it just now the compressor clutch turns when the a/c is turned on, although I haven't had a chance to observe it when the windows are fogging.


    A secondary problem it has is that it only blows air through the vents on the front of the dash, straight out into the cabin. The air flows only very weak out the defrost vent at the windshield or the floor. It does this on all settings. Although this might contribute somewhat to the problem, it seems like the a/c does completely cut out as the windows will still fog hard with the a/c set to on and on full fan. When it cuts off the air in the cabin feels immediately humid. One that that helps somewhat is to turn the temp toward cooler and it seems to not fog as much and gives it a chance to maybe clear the fog some.


    Any idea what's causing this or what I should do to start testing?

  2. #2
    JPNinPA's Avatar
    JPNinPA is offline Senior Member
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    Feb 2009
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    Problem w/ intermittent defrost a/c

    Checking cheap or easy first.
    Make sure the a/c drain is clear. If the water cant make it out, it stays in and gets recycled. Ends up smelling musty. Look at the intake area as well. Jeeps cowl drain can cause buildup to make into the air intake.
    Id have to check but for many cars if there is a vac leak defrost is the default setting. If you have constant bleed-through still may be vacuum. It could be something blocking or bad dislodged door.
    Blend door
    Check your heater core for leaks or blockage. Leak will result in water on the flor and overheating. Blocked core may be cold air or occasional warm air.
    Some vehicles have a valve to the heater core. Bad fuse or relay or valve.




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    Last edited by JPNinPA; 03-10-2019 at 12:53 AM.
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  3. #3
    JPNinPA's Avatar
    JPNinPA is offline Senior Member
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    Problem w/ intermittent defrost a/c

    Keep in mind warm air holds more moisture. In the winter when i drag snow in or rain i may leave the windows cracked to get the moisture out. There are times when I drive heater on high hit with windows wide open.


    Sent from my iPhone using Jeepz.com mobile app
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

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