AC Whirring Sound When On - Compressor, or something else?

Hi, When my AC is on there is an intermittent whining/whirring sound that I can't pinpoint. Its not always apparent and can vary in volume, I would usually expect to hear it in traffic as a humming/quiet-ish whirring which always stops when the AC is disengaged. I assumed this is probably a bearing inside the compressor itself so have ordered a new one along with a new dryer but started to doubt myself. I have tried to listen to it from the back of the car with the engine lid open expecting to hear it clearly coming from the compressor once the clutch was engaged, but it seems at least in this occasion I could hear it more inside the car than I could listening right up close to the compressor, which doesn't seem to make sense? Anyone have any thoughts on what else it could be? Rads/Condensers quite new and clean, AC system pressure tested and re-gassed 9 months ago and blows nice and cold. Just concerned that if it is a failing compressor I want to change it before it seizes and takes the belt out with it.

I have a similar noise to the one you describe, so looking forward to what the experts think. I've done little investigation and have lived with it for years but it's starting to get on my nerves.

It will probably be the fan, drop it and from housing and switch on and see if that is where the noise is coming from, if it is a drop of wd40 could help.

Correct , the fans ( front of car) come on all the time the aircon is on.

My guess would be low gas despite the top up 9 months ago. Whining from the compressor is a common symptom when it is getting a bit low (but the a/c will still be cold - at least at this time of year). Normally most noticeable at low revs - 1500- 2500.

Gas is getting low.

I have the same problem on mine. need to get the gas changed. all new pipes from compressor to condensers and still needing to do it yearly

Thanks for the various insights, I am going to do a little bit more diagnosis to try and pinpoint where the noise is coming from as at this point I am reluctant to think it's low gas based on; I noticed the whirring noise when I bought the car last July. The advice was that he noise was probably due to low on gas/oil making the compressor grumble, so I had the system evacuated, pressure tested and re-gassed from scratch with the correct volumes and the noise wasn't cured, so I had in the back of my mind it must be the compressor internals failing (jumping to conclusions of course)... Didn't use the AC over the winter other than occasionally to demist, and the noise was still present when I did. So now I've bought the compressor and dryer and started to plan the job, but noticed that even though I could hear the noise inside the car, I could not hear anything untoward coming directly from the compressor, which has given me second thoughts... The front fans work fine, after a bit of a blast yesterday I left the engine running on the drive for a few mins and both front fans kicked in on high, pretty noisy but 'healthy' noisy, just spinning really fast and shifting a lot of air for a few seconds before switching off. Would the fans come on low speed with the AC, so it could well be a fan noise, but only when they're on low speed? At high speed the power overcomes whatever friction is causing the whirring noise. I'm trying to avoid evacuating the system again, swapping in a new compressor, re-gassing again and finding the noise is still there! As I said my main concerns is if the compressor is failing I don't want it to suddenly seize and throw the belt off, but it seems at the moment that is not the most likely cause. ..also note a few people saying they have similar and living with the irritating noise for years, so be good to find a common cause/solution.

The fans should run in low speed whenever the AC is on, irrespective of whether the compressor is engaged. If yours aren’t running, I wouldn’t necessarily expect the ‘low-gas’ type noise (groaning from behind the dash, frequency proportional to engine speed) until the system had got up to temperature. Then I would expect it. It’s quite common for the low speed resistors to fail. I say this because mine was consistently making the noise I describe, despite having a leak test and recent re-gas. It was clearly getting worse in traffic and high ambient temperatures. I found one of the fans to have failed.

It might be debris in the ducts or around the HVAC motor. There is some foam lining in places which can degrade and peel away. See my old post here: S Post in thread 'Any ideas what this is?' 26 Jun 2019 I thought I'd wrap this thread up with some pic's for anyone who has the same issue in the future & stumbles across this. Pic below shows the lower side of this flap. If it did previously have a foam membrane layer, then there is no evidence of it or any residual glue. The red arrow in the 2nd pic shows what looks like the same type of membrane lining the inner wall of the chamber. I'm presuming it has a foam backing, based on the debris I found. It appears to be some sort of insulating layer inside the blower motor housing, which only seems to be available to purchase with the whole... sp1ke

Is it engine speed dependent? I had a buzzing/whining noise at 1,800 to 2k rpm that with the help of the garage I eventually traced back to the air con and low gas pressure. In turn this was caused by one of the hard lines having corroded and failed. A new line and a re-gas and all is good. I'd already replaced the condensors so didn't immediately have it down as an AC problem, I thought it was an issue with the front diff (its a C4S).

Gas is low. When I had mine regassed in 2023 as soon as I got a mile down the road I knew there wasn't enough in, so went straight back. My man put another few ml in and it cured it. I've seen various volumes on various sites as to what it should be. Only needs to be slightly down and you can hear alsorts of wacky noises.

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Thanks Alex that's enough for me to take it back and have the fill checked, certainly before opening the system up and all that entails. As I am now focused on the issue, I went for a drive with AC on and typically couldn't replicate the issue that I've had every other day for 9 months! I think getting it back on a machine at a reputable indy (not quick fit) to have the gas/fluid levels checked and topped up is the most sensible first step before cracking open the system. Hopefully I can get a refund on the compressor & dryer and save a few quid unexpectedly, which is rare but nice!

compressor noise is from the back as its on the engine -I doubt you would hear it unless the bearings were damaged Hissing noises are usually from the evaporator(expansion valve) and are usually a sign of underfilling/low charge Have an A/C specialist look for leak using a UV dye We had similar on the GT4 it turned out to be 2 leaks from the connections behind the frunk

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Thanks, the noise isn't coming from the compressor its kind of from behind the dash as a groaning so suspect low gas. The system was pressure tested and held vacuum for >30m when I had it done recently and it groaned straight after the re-gas hence me assuming it must be compressor... Beginning to wonder if just not enough gas was put in? I've seen 850g and 900g spec floating around the internet so it's possible I guess? Anyone know definitively for an OE Denso on 2003 C2?