weird sound happens when air conditioner is on

[firegun9]

Hi,

I have a 2001 LE corolla. The millage is 76000.
The problem is that if the air conditioner is on, when I push the throttle from beginning, I will hear some weird sound from under the hood. The sound is like "KON KON KON," and it KONs only 3 to 4 times. When the car's speed is above 10mph, the sound dispears.

The sound only happens when the car speeds up from a stopped status. Somebody told me it could be a problem of air conditioner oil. The sound itself also sounds like some oil is missing, and something is too dry. I don't know much about cars. Does somebody know this problem?

[retiredat44]

maybe the a/c clutch is going bad and only catcnes at a certain speed..

[90 GP]

If it only does it only with A/C on it could be the belt tensioner or belt slipping under load. Does the car cool down ? You could try leaving the car in park and giving it some throttle while someone looks and listens to try to pinpoint where the noise is coming from.

[firegun9]

Hi 90 GP,

Thanks for the hint of belt tensioner. My belt has never been replaced according to previous owner. So it's alreay 75000 miles. I noticed the belt was very dry before, and I put some wax on it (somebody told me to do that instead of replacing a new one). But I think it only helps for a short time. And even when the car doesn't move, I can tell that the sound from the belt is a little loud and weird. Now I have some direction.

[Crowbar911]

wax on a belt? I have never heard of that before.

what type of wax? carnuba wax? the stuff for the paint?

That would hurt more than help, as wax repels moisture.

[retiredat44]

You can use soap on belts. With the engine off... take a bar of soap, and wet it, then run it lightly over the belt (the part of the belt the runs on the pulleys).
You can also just buy some belt conditioner at the auto parts store.

[firegun9]

to Crowbar911,

yes, it's wax. I turned engin on to let the belt keep rotating. Then I put a candle close to the belt, so wax would be grabbed by the belt. Since the belt is rotating, every part of the belt would get waxed. My friend just told me put some wax on the belt. Turning the engin on is my idea.


to retiredat44,

Thanks for providing wet soap and belt conditioner.


Here is the update:
I checked the serpentine belt. It has some cracks inside and this should be fine according to the information on Internet. It's also aligned well with the pulleys. So I guess it's not the problem.
Then I tried to find out where the growling sound came, and I had some new findings. When I park the car in P or N with the hood opened and gave it a little throttle, I didn't hear the growling sound, even I gave it more throttle. Then I closed the hood, switched to gear D, and gave the car a little throttle to make it move, the sound appeared. Does this still make sense if the problem is the belt tensioner?

[90 GP]

At that many miles on the original belt I would replace it . That would be the way to eliminate it as a cause for your noise and keep from being stranded if it should break. Another thought is you might have a loose metal heat shield on your exhaust system that is loose and rattling at certain speeds.