It sounds like the center vent is opening then slamming closed (or vice versa) about every three seconds. Only does this in one setting, I don't remember which but I can find out. I'm guessing this is a vacuum leak somewhere? Anyone got any suggestions? (besides not using that setting!) This is on a '91 Sovereign.

 

I have recently determined that the center vent works properly and that it is not the problem. The sound was coming from behind the center vent and slightly to the right. I removed the glove box and found that the upper blend airflap motor was making the noise. It sounds like it is trying to open or close a flap and failing and snapping back in to place. You can see and feel this blend flap motor jump each time it makes the "clomp" sound. If left on it will repeat about every three seconds. Should I remove this motor? I am not sure if the problem is with the motor or the flap binding on something. Advice?

 

The feedback pot is on the left side of the vent and sometimes they fail to tell the motor to stop at the correct place (the motor continues to run!!)

Sometimes the flap is very tight and the motor/gear casing cracks and can't reach the limit called for by the position sensor (feedback potentiometer) and the motor continues to run!!

You can remove the motor/gear assy for inspection.

Plug in the electrical connector and move the flap (with the position sensor) by hand and see if the motor stops and moves in relation to the flap position.
If the motor runs, it is supposed to stop when the commanded position is reached. If the motor never stops, then the sensor is faulty.

good luck

bob gauff

 

That is very helpful. Thanks. I will try that tomorrow if at all possible. I believe I can remove the motor/gear through the opening where the glove box was? The first pic shows the opening and the second the upper blend flap motor (outlined in white). This is the part I need to remove and check?

 

Yes! that is the servo motor that controls the upper rotating air duct.There is a lower unit that uses the same part so swapping them is also an option. Remove the A/C control unit (the grand piano looking unit) and it is behind it. The servos are held in place by (2) #1 pozidrive screws.

bob gauff

 

Will I cause any problems by removing this motor from the right side? Will it disconnect something from the left that I won't have access to? Once I have the motor in my hand, I should I check the movement of the flap for binding? If no binding is found, I should manipulate the HVAC controls and see if the motor moves correspondingly, as you instructed? I assume, that if the sensor turns out to be bad the dash needs to come out? If that is the case I think I will live with the bad sensor and unplug the motor. Does this motor/mixing flap control the face vents or the defrost/demist vents? If it is for the windshield I will set it to blow on the windshield if I have to disable it. Thank you again for your help.