Question about Mercury Grand Marquis

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2007 mercury grand marq LS, system always on defrost. AC temp OK, no control to vents,floor or any selections on control panel, Blower fan OK. gchan2@sbcglobal.net geo

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  • George Chandler May 27, 2009

    Thank you for coming back, My problem is I have no control of my vents,floor, max/air,heat. It is always on defrost no mater which buttons I use on the control panel. My air-conditioning operates fine but only comes out through the defrost......geo

  • George Chandler May 28, 2009

    Thanks for your help, This problem started about 4weeks ago, Yeasterday I took it to the ford dealer for an oil change and they said it could the control head on the dash, or door motors, or some type of acuator buryed under the dash. Price 700. to maybe 1200. they have to remove dash board......geo

  • George Chandler May 29, 2009

    Did you have time to think of a solution of this problem, My car has 46000 Mi and hope this is not an ongoing problem with this car. Hope you can help me with this.......geo

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  • Mercury Master
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This problem is caused by a lack of vacuum to the different vacuum motors that control where the air is directed, there are 2 things that cause this problem, one is the vacuum switch is defective in the AC/Heater control head in the dash, the other is loss of engine vacuum to the switch, if u look under the dash on the passenger side (remove under dash panel) you will see a small (1/8" diameter) plastic vacuum hose that comes from the upper corner of the passenger kick panel, this hose which is usually black is the vacuum supply, test it for vacuum, if there is not vacuum go out to the engine and locate it on the other side, it will go to a vacuum reservoir and that will have a hose to the engine which is the vacuum source, if all these show no problem and vacuum is present then the problem is the AC heater control in the dash.

Posted on May 29, 2009

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  • Master
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I believe that your dealer is correct on this one.  Sounds like it is your door motors/actuators.  There has to be a short in the signal being sent from the dashboard controls to the actual motors.  Had the same problem with a Jeep a couple years ago and had to take the whole dash apart and dig around up to my elbows for a couple hours.  That being said, it's not an easy fix and you are probably best having a mechanic help you with it.  If I were you I might check around to other local mechanics and see how much they would charge because that seems like a bit much.  Hope this helps.  Let me know if you have any other questions.  Thanks for rating my response and for using FixYa!

Posted on May 29, 2009

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  • Expert
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It sounds like a vacuum leak from the air intake. When did this started happening? maybe after an oil change....

Posted on May 28, 2009

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  • Master
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Hi there,

The compressor puts the refrigerant under pressure and sends it to the condensing coils.
In your car, these coils are generally in front of the radiator. Compressing a gas makes it quite hot. In the condenser, this added heat and the heat the refrigerant picked up in the evaporator is expelled to the air flowing across it from outside the car. When the refrigerant is cooled to its saturation temperature, it will change phase from a gas back into a liquid (this gives off a bundle of heat known as the "latent heat of vaporization"). The liquid then passes through the expansion valve to the evaporator, the coils inside of your car, where it loses pressure that was added to it in the compressor. This causes some of the liquid to change to a low-pressure gas as it cools the remaining liquid. This two-phase mixture enters the evaporator, and the liquid portion of the refrigerant absorbs the heat from the air across the coil and evaporates. Your car's blower circulates air across the cold evaporator and into the interior. The refrigerant goes back through the cycle again and again.


Let me know

Posted on May 27, 2009

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