Hi Frequency whine/whistle with AC on -- LS

[goats]

I've noticed on both my cars, a rather high frequency 'whine' with AC on , generally during the compressor cycle. It must be about 5KHz or so, kind of like the high frequency whine given off in the flyback transformer of old TV sets-- not really bothersome, but there nonetheless.

Anyone else ever notice this? I am wracking my brain trying to postulate on the source of the noise. Whatever is causing it, must be small (freq is pretty high for a mechanical system). Its not the fan or being generated by air movement in the system per se, because it does not exist in econ mode. Could it be a whistle, resonation associated with the phase change from liquid to gas?

MistaLava, Mr T, Steve, anyone with good ears--- does anyone besides me hear this?

[Mistalava]

I'll make it a point to give it a listen, Goats. I still get a "chirping" noise at times from the dash when the AC is on and I accelerate (maybe the fan touching something as the weight is transferred). Hey, your ears are still good if you can differentiate 5 kHtz ;-)

[MrT]

I had such a noise in one of our cars. It kept me from using the A/C because I am particularly sensitive to such things. I guessed that it was a resonance in the A/C expansion orifice, but only because I used to whistle by holding pieces of cellophane or a blade of grass tightly while blowing over it. I have no evidence that this really _is_ the issue, but only a suspicion. If so, then you should be able to fix it by swapping out the expansion valve. Not a cheap enough activity to use as a speculative fix. You could try the hose stethoscope trick to check whether the expansion valve is a concentrated source of this frequency, though. Or maybe a microphone and a (audio frequency) spectrum analyzer? Such things might be available on a laptop PC these days. Could be real handy.

Michael

[RexCars]

It sounds like failing bearings in the fan motor. Look on the website and find the link Alfa Steve posted to the place that sells a Saab 9000 unit for less than $100 rather than getting the much more expensive one for the Alfa. You will need to R&R the fan from the old unit to the new.

While you are in there, best replace the heater core if you haven't recently.

Rex

6 months on Goatster's LCD panel and going strong.

[goats]

Does not happen in econ mode no matter what speed the fan is running at.

[Rorysbrown]

I've think I'm hearing this too on my '94 LS Black Automatic I just picked up a few days ago.

[Alfissimo Int.]

Quote:

Originally Posted by goats I've noticed on both my cars, a rather high frequency 'whine' with AC on , generally during the compressor cycle. It must be about 5KHz or so, kind of like the high frequency whine given off in the flyback transformer of old TV sets-- not really bothersome, but there nonetheless. Anyone else ever notice this? I am wracking my brain trying to postulate on the source of the noise. Whatever is causing it, must be small (freq is pretty high for a mechanical system). Its not the fan or being generated by air movement in the system per se, because it does not exist in econ mode. Could it be a whistle, resonation associated with the phase change from liquid to gas? MistaLava, Mr T, Steve, anyone with good ears--- does anyone besides me hear this?

[Mistalava]

Hey Goats, no hf noises on my car with the AC. I listened with and without Econ and under different engine and AC fan loads. Sorry not to be of any help.

[romroc]

I hear the same nose on my '93 L. It's not a loud sound, but persistent, and only when the A/C is operating. At other times it's not apparent, only when the outside temp is very high do I hear it. Italians apparently want you to hear the A/C when it's on.

[AlexGS]

Presumably this is not the noise made by the cabin temperature sensor fan, since I think that would run in ECON mode as well (not sure though).

The temperature sensor fan is usually in the ceiling console but sometimes in the dashboard (with a small intake hole near the steering column, perhaps only on early right-hand-drive 164s like the one I saw last week). The brushless motor usually emits very little noise and if seized, would probably be silent (but possibly emit a whine?)

-Alex

[MrT]

In searching for sources of noise, you have to consider the power sources involved. There is no high frequency oscillator in one of the brushless fans, so not much chance (qualified statement) of that being the source. A high frequency sound coming from a mechanical source would require something small (to keep the wavelength short) and high-pressure (to supply the energy to keep the oscillation going.

The Bosch LJet Spiders have a manifold pressure sensor with a few cm scale size and a few psi of pressure drop. When the (thin metal) wall cracks, it forms a whistle powered by the manifold vacuum. Really high frequency and very annoying. Roughly another octave or two above the highest "A" of the piano keyboard by my ear. Middle "A" as I recall is 440 Hz, and there are four more A's on the upside of the board running to 7 kHz. This would put that nuisance frequency at or above 2^5 * 440, or about 15 kHz.

That's about as close as I can come to estimating that frequency by pitch memory (I do _not_ have perfect pitch). The A/C whine is in the same ballpark of frequency, and maybe a bit lower. For what it's worth....

Michael

[Alfisto Steve]

It maybe the rotating group and bearings inside compressor as that is where the noise is in my 93L when I engage compressor. Sounds like a super charger whine. I have added 2 oz can of oil charge to it as system converted to R134 before I got car and blows cold so I am hoping compressor will stay working and just make people thing I have fast CAR.

[AlexGS]

Quote:

Originally Posted by MrT In searching for sources of noise, you have to consider the power sources involved. There is no high frequency oscillator in one of the brushless fans, so not much chance (qualified statement) of that being the source.