Sound changes pitch with air

[zheka]

Hello. I just noticed when I turn the AC from low to high, I can hear the sound behind the front dash, increasing or deceasing it's pitch with the amount of air pushing through. The higher the faster air speed setting, the higher the pitch, but still pretty low pitch, not a whining sound. Same sound when AC is off, or ignition is off (just accs on). If anything I can try to record video with sound, to maybe better explain.

What drives air through the vents? Is the AC compressor pushing air, regardless if AC is on or off? It almost sounds like a bearing is bad. But i'm not sure how AC works. Not a mechanic.

Any idea?

Thank you.

[centralcoaster33]

The air is pushed through past either the heater core (which is hot and heats the air as it passes) or the AC core (which is cold and cools the air as it passes) or neither (this just circulates the air at whatever temp it is) by a fan. The fan changes speeds to increase volume/ flow. They are a motor with fan blades (well, it's often more of a fan cylinder shape than a propeller shape) and do have bearings in them. The motors can wear out and or the bearings can wear out and this may make a sound (some people describe this as a whining type of pitch and others hear a hum). Where does the noise originate from? Under the glove box? Try and listen with car off and air on max or something. See if you can even 'feel' the noise by touching the parts under the dash.

We do have the FSM with instruction for diagnoses if you'd like to get into it.

Please let us know how it goes and welcome to NICO Club!

[zheka]

Thank you for the response. So after trying to isolate where the noise is coming from, it almost looks like it's coming from below the windshield, and you can hear better from under the hood.

I took a video, to show what it sounds like. Engine is off: https://photos.app.goo.gl/9n4IquolM644ojKn1

When trying to feel around, it seems like that plastic trim, that's below the windshield (with all the swiss cheese holes), you can feel tiny vibration on it. But no vibration on the engine.

[centralcoaster33]

Well, I listened and watched. It just sounds like a motor is turning. It probably is the blower motor turning. See if you can hear similar sounds up under the steering wheel, near your brake pedal. See if the sound changes the same when you adjust the air speed. I'm suspecting your blower motor, but I could be wrong. The motor is by the brake pedal. The ductwork goes up to behind the hood where you hear it from the outside. I'm wondering if you can hear it from the inside as well. Also, what year is this Rogue? I don't see it posted and I'm looking at instructions for a 2012.

[Rogue Jarhead]

Something probably fell down your defrost vent. Leaf, paper, or other foreign object that is now rubbing on your fan.

[centralcoaster33]

Oh, that's a good guess! Zheka, below is a link to the instruction book. You'll probably have to take apart a few things to get into your ductwork and fans so that you can fix the issue. The instruction book (FSM, Factory Service Manual) will have it all detailed on how to do it. You'll just need time and some tools or to hire a mechanic.

http://www.nicoclub.com/archives/nissan ... nuals.html