dann928

Hello all,

02 C4S manual 80k mls
Recently I've noticed a strange noise/groaning/whirring sound from the front end while the A/C(just a/c not the actual climate control) is on. The noise only happens or is audible when passing through 1200ish rpm when coming to stop. During idle the noise will stay until I accelerate again. The noise is not present at any time with air conditioning button switched off or when cruising.
I read in other posts that this may be related to a radiator fan but the other posts didnt mention anything about the a/c compressor being on or off.
Any ideas?

Thanks.

DBJoe996

Noise from front end as you have described is a bad radiator fan either left or right, or both. The radiator fans operate under any number of scenarios, from plain engine heat, high ambient temperature, A/C on, defroster on, etc. Get it checked out.

Macster

As DBJoe996 suggests it could be a bad radiator fan motor and you should check for proper and quiet fan operation.

I'd add that you want to check the power steering fluid level.

I would also add that I've heard a similar noise from the front of my Boxster under similar circumstances -- though I'm pretty sure in all cases the A/C has been on and the compressor active (the snowflake symbol lit on the A/C control panel display) -- and the radiator fans are working just fine and the power steering fluid level is fine too.

I have no real idea of what causes the noise but so far -- so far -- it seems to be harmless.

Still you should check into it.

dann928

Thanks guys.
I checked the fan operation and everything is smooth and quiet. p/s fluid is good as well. I'll have to take it in and see if the techs have an idea.
With the 110+ degree temps here, I really need to trust my a/c haha.

PelicanParts.com

Sounds like it could be the EVAP core. If it is there will be a weird smell and I've also noticed a hissing noise before on a few cars before the AC quit working. Otherwise, it could be low on refrigerant. If it is low there might be a leak somewhere that needs to be diagnosed.

dann928

Thanks again for the info. I've got no strange smells or hissing so thats a good thing I guess.

dann928

Here's a video of the noise I'm hearing. Just wanted to let you guys take a listen for yourselves.

5CHN3LL

It only happens when the compressor is on, and it's variable-speed (and thus seems belt-driven) - so I'm guessing the compressor bearings are shot. Are you CERTAIN it's coming from the front end? If so, obviously, it isn't the compressor, but the fact that it (at least seemingly in the video) is directly tied to RPM makes the compressor seem like the culprit.

Macster

While I doubt it one can hope with the compressor on this somehow loads the belt drive system and there is a noisy idler roller bearing making that noise.

Granted a very long shot.

Much more likely is as 5CHN3LL offers the compressor is at fault. Bearings or something else but inside the compressor.

It will not fix itself and can only get worse with more use. Time to seek out a reputable A/C shop in your area and either have the compressor rebuilt if that is a viable option where you are or have it replaced.

The system should be evacuated first to remove the refrigerant and whatever oil comes out. If there is debris in the system that really complicates things.

The repaired or new compressor fitted and any seals/o-rings renewed then the system evacuated again and checked for leaks then refilled with the right amount of refrigerant and compressor oil.

Then the system tested to ensure it blows cold relative to the ambient temperature.

dann928

Ok, I've had the car to the shop and had the ac checked. We did determine that the noise is from somewhere in the dash/front not from the compressor. Had the a/c evacuated and the drier changed, it seemed to be the original factory drier and was a mess (I guess its common here for shops and dealers to overlook something as simple as the drier canister). After all said and done the noise is still there but definitely less frequent and quieter. I think the noise is some bearing or something on the fan unit/ air box in the dash. I guess I'll just leave her be until or if it fails.

5CHN3LL

Well, the good news is that you're in Dubai, so how often do you actually need to use the AC? Once or twice a year, tops?

dann928

Haha, yeah at the moment its quite hellish outside. You cant live without a/c but luckily I try to not drive the car too much in the summer. The ac is strong and the car stays cool at 115+. I do enjoy some windows down cruising in the winter though.

TheBruce

Hi - was there any conclusion to this? I have the EXACT same noise in my 2006 997 and I've been trying to track it down for a year. It only happens during idle or when coasting to a stop light. Previously it would stop immediately if I turned the AC off or would fade away by itself after 10 seconds. I thought it might be a bad AC clutch and took that off to inspect it. I found the clutch plate was cracked and figured that was the problem...unfortunately it wasn't. I replaced the compressor clutch pulley and the sound came back. Whats more is since changing the clutch out when I turn the AC off the noise wont immediately go away like before. I'm baffled.

Similar to dann928, I cant hear the noise with the engine compartment open. I can only hear it in the cabin and it seems to be reverberating off something. With the change in behavior after swapping out the AC clutch my next best theory is its something to do with the belts, possibly the belt tensioner reverberating. The could make sense as the AC on/off would put different load on the belt.

The other theories are...

- ac blower fan under the dash, but it sounds like its coming more from the backseat area, not dash
- low refrigerant causing some reverberation in the pipes
- reverberation from radiator fans, but they sound ok when outside the car
- bad bearing on the engine compartment fan, but sounds ok when outside the car
- alternator overrun pulley

Any follow ups appreciated. Sounds like this is an issue across 996/997/986.

TheBruce

Just to update my findings here. After 3 days of testing and no more noise, its looking like this issue is caused by the AC system being low on freon. This must cause a reverberation somewhere in the AC lines that transmits into the cabin. I added some R134 and while it was within pressure range, it was on the low end of the range. I added half a can and haven't had any noises since.

Prior to this I checked the alternator pulley, belt tensioner, and condenser fans. All sounded good.

Im hoping to put this 12 month mystery to bed.

scritcha

i know what it is not
alternator freewheel pulley, other belt pulley/tensioner
leak in system; it holds gas and has been recharged.
rad cooling fans as it is rev sensitive at low revs anyway

car has had noise for 8 years and although in UK it is not used too much, I am sure it is not the comp; it should have packed up long ago if it was a bearing or sliding vanes.
cant be heard outside the car
seems to vibrate in the cabin, maybe form the front but not sure
aircon works fine so cant be undercharged, not by much anyway

i am totally out of ideas, seems I am not alone though