Question about 2001 Jeep Cherokee

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Air will not come out of a/c vents

I just had a bad radiator fan so I changed the fan motor and the modual that is found under the rt headlight. The fan works however I can only get air aout of the defrosters, The air direction control does not work.

Posted by mwwohlgemuth on

  • mwwohlgemuth Jun 18, 2009

    Sounds like you are on the right track, I do not hear any hissing noise, And I followed all vacuum lines that i could find, From the canaster under the headlight to the fire wall and over to the left side of the engine. I would think that the problem is in the area that I had apart, under the battery ao headlight?

  • mwwohlgemuth Jun 18, 2009

    I recently replaced the radiator fan motor and the electronic controller which is found under the right headlight. After I put it all back together The air flow control does not work. The air comes out of the defrosters nomatter which position the knob is set. The off position does work.I took it apart again and tried to find a broken or loose vacuum hose but all looks OK, is this the only posible solution? I do not expect it to be anything under the dash, I did not fool with anything there.



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Put old parts back on

Posted on Jun 18, 2009



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When you say the vents do not open, I am assuming you mean no air comes out the vents, but does come out the defrost and floor vents ok.

I would first look to see if there is a broken vacuum line going to the dash from under the hood. Listen under the dash board for a hissing noise to indicate that there is a vacuum leak in the dash. This system should be using vacuum from the engine to open and close the air diverter door inside the dash.

If there is no vacuum from the engine to the dash, or if the valve in the dash is leaking that vacuum then it will default the diverter door to blow air out the bottom and top vents only.

I would open the hood and look at listen (with the engine running) for a vacuum leak from either a broken vacuum hose or from a plastic connector attached to a vacuum hose. If you don’t see or hear anything under the hood, move inside the car and listen and look under the passenger side of the dashboard for a hissing noise or an obvious hanging rubber hose.

There could also be a chance that the diverter door itself is either broken or restricted. I have seen a pencil fall in the vents on top of the dash, and block the diverter door from moving. Inspection of the diverter door and the vacuum control valve will require dash removal which you will want an experienced mechanic to perform.
The problem is causes by a broken vacuum line. These lines are all over the engine compartment, but those affecting the A/C are between the engine and the firewall behinf a vanity plastic over.
Thanks for contacting Fixya

Posted on Jun 18, 2009

  • e-Guru
    e-Guru Jun 18, 2009

    This occurs because the climate control doors(that direct the ventilation in the car) are vacuum operated, using intake manifold vacuum. The default(no vacuum) position directs the air to the defrost outlets. When you accelerate, the manifold vacuum drops below that required to operate the doors, and whatever you've got the temp set at blows out of the defrost. When you take your foot off the pedal, (or release the cruise control) the vacuum quickly recovers and the ventilation returns to normal.

    Also ,

    It's proberbly the sensor that controls the front vents from opening. And it's stuck in the closed positon. You might try they have a very good and easy system to use for trouble shooting, and they also give diagrams. I found them of great help because they go into great detail in their diagnosis.

    Thank you



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