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Thread: Weird HVAC Issue

  1. #1
    Join Date
    Jan 2023
    Location
    Abington, PA
    Age
    54
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    Weird HVAC Issue

    I have searched quite extensively and not found this issue here. I had to replace my Blower Motor Controller and did so with the aftermarket harness upgrade. Since doing this (a couple of weeks ago) I have had this happen twice... with my HVAC turned OFF completely, it still blows air. Not out the vents, but it seems to be behind the dash. The fan switch does nothing, the OFF button shuts off the head display, but no change in air. And the AUTO button changes nothing with the air either. The only way I have found to turn it off, is the turn the car off. Then it's fine. Anything from the experts?

  2. #2
    Join Date
    May 2019
    Location
    Harrisburg, NC
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    53
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    401
    Have you done a self test to see if there are any codes?

  3. #3
    Join Date
    Jun 2011
    Location
    Northeast OH
    Posts
    8,041
    Check your vacuum lines. The black box on driver fender under hood is the vacuum reservoir. Vac lines get old and brittle over time. Also the eatc O rings get dry and hard and then will only blow out the defrost
    2004 SB Ported Trilogy 48
    Has supporting mods and stuff
    Thanks to Marty O for his help in updating this car.

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    Rex "SC Cheesehead"

  4. #4
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    What is the manufacturer of the BCM? You should only use a Motorcraft replacement as all others are crap.

    Why did you need to upgrade the BCM harness? I've never seen one go "bad".
    “When you can’t make them see the light, make them feel the heat.”
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  5. #5
    Join Date
    Jul 2010
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    Crook County
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    Check the vacuum lines behind the dash. I had that same issue, I thought it was the blend door actuator, ended up replacing it with oem but Zack had discovered a crack in the vacuum line which was causing air not to come out the vents and I believe that's what caused air to come out the defrost while the eatc was off. Already had the eatc o rings fixed too at the time.
    300A 8-20-02 #3849
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  6. #6
    Join Date
    Jan 2023
    Location
    Abington, PA
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    54
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    The problem is, it blows with ac head turned off. When it’s turned on, it blows correctly.

  7. #7
    Join Date
    Nov 2021
    Location
    Florida
    Age
    66
    Posts
    2
    Had similar problems. My mechanic replaced Blower motor controller. Had a nice cool ride for 10 mins, then ac would randomly go on or off and switches where useless. My mechanic said they have problems getting aftermarket units that work and he usually has to return them several times before he gets a good one. Am getting use to back to the 50's riding the windows down.

  8. #8
    Join Date
    Jun 2007
    Location
    Whitehall, PA
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    2,969
    is it possible the blower motor relay is stuck on?
    2003 Black - sold, back again, and sold
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