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  1. #1

    Default 1984 Fox HVAC vents not working?

    I had a bad heater core and blower motor, replaced them. Tried using the heater and I can hear the blower motor turn on and increase/decrease with the controls, yet there is not air of any kind coming out of any of the vents. I checked the vacuum hose in the engine bay and it has vacuum. Itís getting cold now and I need the heater.
    I donít know if the vents work prior to the heater core/blower motor.

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  2. #2
    Moderator wraithracing's Avatar
    Join Date
    Jun 2010
    Grand Junction, CO/RR TX


    Is your car Factory A/C or Factory Non A/C?

    If factory A/C did you connect all of the vacuum lines to the blend door actuators? Is vacuum getting to the HVAC control unit? Does the unit route vacuum to different blend doors as you move the lever? Is the HVAC box cleaned out of any leaves, debris, etc.? Is the blower wheel filled up with debris, etc.? Is the blower motor wheel correctly attached to the blower motor?

    Default should be air coming out of the defroster vents. My guess is there is something clogging the HVAC box and/or something wrong with the squirrel cage on the blower motor. Good Luck!

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  3. #3


    I'm "pretty sure" that you have a similar HVAC setup as the 86-93 Stangs.

    See the following:

    Name:  mustang88AC_Controls.gif
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    Name:  Mustang_AC_heat_vacuum_controls.gif
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    IIrc, the cable controls the hot/cold selection.
    The vacuum controls where the air will go.

    So, if you have the blower motor on high, you should get air somewhere.
    If it's hot/cold, that is dependent on the cable and the heat-selection door.
    Where the air blows out, is dependent on the vacuum and the air direction doors.

    Good Luck!
    Last edited by stangPlus2Birds; 09-27-2020 at 09:49 PM.

  4. #4
    FEP Power Member
    Join Date
    Nov 2007
    San Mateo, CA


    The vacuum controls look a little different on the 87-93 but they basically work the same. The hvac box is the same.
    Fox Body/3rd Gen MCA Gold Card Judge
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  5. #5
    FEP Supporter tbirdman's Avatar
    Join Date
    Dec 2006
    Middletown, DE


    I know you said you checked the line in the engine bay and said you had vacuum, but did you check to see if you have air coming out of the dash defroster vents? If there is a loss of vacuum between the HVAC box and the ac vacuum reservoir on the fender side of the right front apron, then the air comes out of the defroster vents by default.
    If they take my stapler, then I'll set the building on fire...

    85 Mustang GT

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