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A little help please...

Discussion in 'Chevy Trucks' started by 79Chevy, Oct 9, 2003.

  1. 79Chevy

    79Chevy Junior Member
    Messages: 29

    Today in Houston, TX its been raining all day.....
    I took my truck out and I cant seem to see through
    the window, ya wanna know why?

    MY DAMN defroster doesnt work!!!!!
    My heater works and my vent works.....
    There is air coming through the all the vents, except
    the defroster vents on top of the dash....

    Does anyone know what might be the problem or
    a way to fix it so that air will come through the defroster

    Any input will be appreciative!!!

  2. 75gmck25

    75gmck25 Senior Member
    Messages: 119

    The defrost valve vacuum motor is the one that is just above and to the right of the accelerator pedal. You can reach or look under the edge of the dash and see the vacuum line and motor.

    You can use a gauge to check for vacuum and verify that the dash control is working. You can also pull vacuum on the motor and see if you can switch it between defrost and heat modes.

    I tried to figure out exactly how the vacuum control system works, but I can't figure out the state table in the repair book. There are about 6 vacuum ports on the back of the dash control and it switches various ports in and out as you move the slider.

  3. wyldman

    wyldman Member
    Messages: 3,265

    Does it have AC ? If it does,then you'll have a vacuum motor setup.If not,it will be cable operated.

    There is a defroster duct that goes up to feed the vents right behind the glove box.Maybe it has fallen off or is partially disconnected ?