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Discussion Starter · #1 ·
Let me start off by saying, I'm new here... I'm*not even 100% sure if this is the correct place to post this.
Also, I have 0% experience with the mechanics of automobiles. The only maintenance I can perform is changing my wiper blades, and topping of my windshield fluid, like a pro I might add. Basically, all of my knowledge has been obtained from a friend of mine who is a mechanic. He has told me that the car is really nice, especially for the amount of money I paid for it. I purchased it used, and the previous owner made a ton of modifications to the car. The car came with a folder over an inch thick, full of receipts for all the parts, modifications, and service he had preformed. However, being a complete idiot I lost the folder! I know... It's bad, I have beaten myself up over it on more than one occasion.

Finally onto my question,
I bought the car in October of 2016, hence never really needed to run the air conditioner. Fast forward to late spring, I finally kick it on for the first time. Car is at an idle, and a loud helicopter like sound, along with vibration came from behind the dash. The sound was loud enough to make it hard to hear the radio. However, AC works great. It's cold and all vents work fine. I turn it off, noise goes away immediately. I turned it back on, same noise and vibration. I left it on, and decided to deal with the noise. As soon as I pressed in the clutch, the noise/vibration completely stops. As I am driving, noise is still there, but not as loud. I have no idea what the issue might be. I've been researching this issue quite a bit, and I haven't come across anything that is similar. My mechanic thought I might need a need clutch, after I explained the problem to him. However, after he drove it he isn't 100% sure, he said maybe it an issue with the clutch pressure plate. I've never experienced any issues with the clutch while driving, with or without the AC running. Knowing replacing the clutch is a costly and time consuming repair, I figured maybe I should try and do some research.

Has anyone else encountered this problem?

Any advice will be much appreciated, so thank you in advance!
 

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2007 B6 Passat 2.0T, 1994 E36 M3 3.0L, 2004 Silverado Z71 5.3L
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Let me start off by saying, I'm new here... I'm*not even 100% sure if this is the correct place to post this.
Welcome to the forums, you're in the right place!

The car came with a folder over an inch thick, full of receipts for all the parts, modifications, and service he had preformed. However, being a complete idiot I lost the folder! I know... It's bad, I have beaten myself up over it on more than one occasion.
That is VERY unfortunate because if you still had that folder we could put this to rest right now. While there *could* be a pending mechanical failure as an explanation I'd like to offer you the first, possible more likely, and most innocuous possibility, which you will probably find a much nicer alternative!... The helicopter noise you describe when the AC is very common on vehicles modified with single mass flywheels (as opposed to the dual mass flywheel fitted form the factory). It is a rotational noise (helicopter noise) because the flywheel natural spins, no surprise considering its namesake. If you listen very closely you may even pick it out with the AC off now that you know what to listen for, or you may not. But if there is a single mass flywheel on the car that noise is there even if you can't hear it, trust me. It's just amplified significantly by the AC being on and even more so if the car has stiffer trans/engine/subframe mounts that propagate the noise.


Edit: My advice would be to reach out to the original owner, if possible, since you lost the documentation and ask if there is a single mass flywheel installed on the car. If the owner installed an upgraded clutch/pressure plate combo it is highly likely he also had a single mass flywheel included as well. Popular decision among modders. A single mass flywheel is lighter and also less prone to failure than the dual mass flywheel which is essentially two single mass flywheels bolted together with springs in between to rebound and dampen torsional forces (that's car talk for "absorb vibrations so you, the driver, don't perceive them while driving"). A single mass flywheel does not do so. Also as the single mass flywheel is lighter there is less inertia on the flywheel and since the flywheel is on one end of the crankshaft that directly translates to quicker revving engine (also a quicker decelerating engine to). You'll notice less "rev hang" when you get off the gas since the flywheel carries less inertia after power is cut. The downside of the single mass flywheel is the added noises, a byproduct of all the stuff discussed above, and a not as well balanced crankshaft since one end is lighter than designed from factory (unless the owner also had a lighter weight crankshaft pulley on the other end, but even then it's a bit of a guessing game whether it would be totally balanced without removing it all and checking rotational balance with equipment). In any case, the "less" balanced crankshaft thing isn't THAT big of a deal. In most cases it never really becomes an issue, even down the road. So, that being said, as long as you can live with the noise you will be fine, assuming it is all because of the single mass flywheel, which seems a likely scenario to me. If it is you really only have two options if the noise is too much for you to tolerate: Option 1 - remove it as well as the clutch kit that was designed for SMF use and go back to factory setup (which may be a bad idea if the car is modified to the point that the stock clutch cannot hold the torque it produces... we can talk about that more if you are interested) OR install an upgraded clutch kit that is designed to retain the DMF (like the HS Tuning RSR clutch kit which I can personally attest to being EXCELLENT in every way if you want sportiness and serious power holding without the noise). Option 2 - a **** ton of noise reducing foam (like Dynamat) all over the dash and firewall to try to block out as much as possible from getting to your ears in the cabin via the dash. This may or may not really work well.


Edit 2: If it is not possible to reach out to the previous owner you may be in luck and have a flywheel inspection hole on the underside of your trans. It might be plugged or it might be open. It might also not be there at all (I'm not sure that all 02M/02Q trans have this hole but I know many do). If you have one you may be able to use a snake cam or some such to inspect the flywheel through that hole, enough to determine if it is single mass or dual mass.


Hopefully you made it through all that, probably seemed like a lot since you are new to cars. Hope it wasn't too much. I'm on here not just to help but to try to educate, I enjoy doing that, so felt I should explain how some things work while I was at it. I also have some more general advice for you as a new owner of a modified vehicle, and a VW in general, but I'll save that for a later post. Just don't let me forget!
 

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Discussion Starter · #3 ·
Thank you so much for your help!
Also, I'm very appreciative of you taking the time to explain everything to me in great detail. I will start with taking it back to my mechanic, maybe he will be able to see what type of clutch it is. I will also try and locate the previous owner, or again "the folder" (miracles have happend).
Thank you again, and I will update you with what I find out, fingers crossed it will be good news.
 

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Uhh I'm pretty sure the mechanic is talking about the A/C compressor clutch, no? And not the engine/transmission clutch? Edit oh wait nm you meant if you disengage the motor's clutch then the noise goes away?

Hmm, this helicopter noise, is it like a low whirring that can also be likened to a motorboat noise? If so it's almost certainly low refrigerant charge. Not low enough to cause the car to disable the compressor (low pressure protection) but low enough that it makes such a noise. If, OTOH, this noise is a high pitched whirring noise, then that's not it either.
 

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Uhh I'm pretty sure the mechanic is talking about the A/C compressor clutch, no? And not the engine/transmission clutch? Edit oh wait nm you meant if you disengage the motor's clutch then the noise goes away?

Hmm, this helicopter noise, is it like a low whirring that can also be likened to a motorboat noise? If so it's almost certainly low refrigerant charge. Not low enough to cause the car to disable the compressor (low pressure protection) but low enough that it makes such a noise. If, OTOH, this noise is a high pitched whirring noise, then that's not it either.
Helicopter noise (nicknamed "chatter" by most) is an absolutely classic noise when the AC is on if you have a aftermarket lightweight single mass flywheel and considering the fact that this guy's car has a history of many mods there is a solid chance there is such a flywheel fitted on the car. The fact that the noise goes away as soon as he presses the clutch pedal down, thus disengaging the clutch disc from the flywheel, is just further evidence for this. Before he considers anything with the AC itself he should absolutely investigate what kind of flywheel he has.
 

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I'm having a real hard time trying to figure out what the clutch that disengages the engine from the transmission and the a/c have to do with one another.....? They are completely separate systems and have 0 effect on each other. Can someone enlighten me???
 

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I'm having a real hard time trying to figure out what the clutch that disengages the engine from the transmission and the a/c have to do with one another.....? They are completely separate systems and have 0 effect on each other. Can someone enlighten me???
You guys are missing the point entirely. It has nothing to do with the clutch in AC or trans (not directly), it has everything to do with the flywheel. When the AC is on it adds load (notice idle RPMs rise with AC on) and that load which manifests in NVH is transmitted elswehere like all vibrations, and the stock DMF filters most of it out (for reasons explained in my first post) while the SMF does not whatsoever. That is the main reason you get more NVH from AC. As for the helicopter noise: again it is NOT the AC itself nor a clutch for AC. It is the SMF rotation you’re hearing and it is being transmitted as noise to you with the rest of the additional NVH you’re getting from the AC being on as explained above. If you understand all that up to this point then the reason that it stops when you press the clutch pedal in should be apparent.

Any nore clarification needed?
 
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