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2003 Jetta whistling - goes away when I turn on the AC

Hi Cartalk, you must be sick of me by now! I’ve tried googling this problem, but it seems most people start having problems when they turn the AC on, not off!

My car has a whistle that happens mostly when my foot is on the pedal, but also sometimes while driving at high speeds.

The AC has not worked since I bought the car a year ago; it blows but doesn’t get cold. The whistling stops immediately after turning on the AC and it doesn’t come back. We replaced the serpentine belt because it was cheap and easy, but it didn’t fix the problem as the whistling starts right up after turning off the AC.

My “defered maintenance” solution is just to leave the AC turned on, will this hurt anything other than mpg?

Amanda, if you drive less than 12000 miles a year you are a candidate for low cost leasing so you can have a dependable car.

Where is the whistling emanating from?
Is it…from under the hood…or from the area of one of the wheels…or from underneath the car…or from the dashboard…or…?

Without hearing the sound, the first suspect in my mind would be the AC compressor clutch assembly. If the bearing in the pulley is failing, its vibrations could be getting damped by the rest of the compressor assembly when it’s engaged.

See if with the hood up you can isolate a specific source of the noise. A "mechanic’s stethoscope, usually less that $20, can be a big help. It’s basically just a metal rod made of a metal that carries vibration well, that pushes a diaphragm that creates sound waves that are fed into earpieces. It converts the vibrations into sound waves. By touching the AC compressor (and other parts) with the rod, you should be able to hear the screech much better. BE CAREFUL not to stick it into spinning things. It is, after all, a metal rod.

I personally don’t think leasing should be considered an option. It won’t give you anything at all except a monthly payment with restrictions and mandatory maintenance. Once the lease is up, they’ll come get the car and you’ll have nothing, nada, zip, no car and no equity. And if it has any dings or scratches, you’ll have to pay the full freight to have them repaired by a professional body shop. Even then you won’t own the repaired car. You’ll have to pay the repairs and they’ll keep the car.

The whistling could be wind coming around a window or door that stops when you pressurize the interior with the A/C blower. Does it also stop when you turn off the A/C and turn up the heater blower>

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The car makes the noise when parked if I rev the engine, so it’s not wind (I wish!)
The noise goes away only when the ac button is pressed, if just the fan is on it still makes the noise.

Please allow me to ask again

Another idea, when the AC is on, the under-dash HVAC fan’s air flow path may be changing compared to the AC off condition, b/c the vent doors are moving around depending whether the AC is on or off. You know how a flute works, putting your fingers over the holes changes to the tune it makes, right? Might be something like that, the sound is coming from air flow disturbances in the hvac duct work. Sometimes it isn’t that difficult for a shop to poke around in the duct work, sometimes they’ll l find some leaves or twigs causing air flow disturbances, or the debris will be be interfering w/the blower’s fan cage. The stuff gets in there from debris collecting in those vents under the windshield.

You will have to open the hood and identify the source of the noise. This is the third thread on the whistling noise and we can’t hear the noise. Perhaps you can post a video of the failing A/C clutch with the A/C on an then off and we can observe the noisy clutch.

Another possibility is that it’s coming from the cooling fan. Most cars today have two electric fans, one that responds to the engine temp and one that turns on when the AC is engaged. The AC fan ensures that air is passing through the heat exchanger that dissipates the heat from the compressed refrigerant. In an AC system it’s called a “condenser”.

You’ll need to peek under the hood.

A stethoscope like @the_same_mountainbik mentioned is a good idea, but if that has no results…some people just don’t have the knack for this.

Try this. Find a 2 foot piece of old garden hose and a small 6 inch funnel. Stick the funnel in the far end and put the other end to your ear. Then move the funnel around in different areas under the hood to at least find the general area of thew sound you are hearing. Then you can either use a stethoscope as @the_same_mountainbik suggests, or just remove the funnel and use the hose alone to pin point where exactly the noise is coming from.


It is coming from the serpentine belt area, but beyond that it’s hard to pin down which specific area of the belt. I’m assuming it is coming from the ac compressor but couldn’t say for sure.

The AC compressor would be an excellent guess. The “mechanic’s stethoscope” should amplify it enough to “nail it down” if it is. Just touch the probe to the compressor’s housing and, if that’s the culprit, you’ll hear music in your ears.

I actually have a medical grade stethoscope, would that work or would I risk damaging my ears?
Also, let’s say it IS the ac compressor, do I have to get it fixed? I don’t really want to drop $600 if it’s not hurting the car

It should work, but be very careful. A probe is probably safer that sticking your hand in there trying to lay the medical stethoscope on the body of the compressor.

It would work, but the biggest problem can be getting hair, or jewelry, or clothing entangled in the serpentine belt when the engine is running. If you have long hair, tie it back. If you are wearing a necklace or a scarf, take it off. If you have long sleeves, roll them up.

Excellent thoughts, VDC. I “second” your motions.

Thank you.
Lest we forget, Isadora Duncan was killed when her very long scarf got caught in the wire wheel of the roadster in which she was riding. Something similar could happen just from leaning over an engine when it is running.

Oh man, that’s scary. I think I’ll look into a mechanics stethoscope. But what if it is the ac compressor, can I just ignore it?

If you’re willing to run the risk of having it seize (it might be bearings) and pop the serpentine belt, leaving you stranded in a bad part of town on a dark and rainy night, you can.