Hello,

something bad happened today with Octavia 2 2012 1.4 TSI. I was driving in the city, with the AC turned on, when the car suddenly did a loud clunk sound. From that moment on, a loud vibration was to be heard and felt. At first, I thought it was related to suspension/steering, but after turning off the AC, the vibration disappeared. When turning the AC back on, the loud vibration resumed. Regardless, the blower/fan works fine with AC turned off. Until now, this sounds like some AC issue, but I think that I can also feel now a bit of the same vibration at idle, or when driving very slow in first gear. I'm not 100% sure about this last part, though. 

Any idea what went wrong?  The vibration at idle is maybe just in my mind, I need to do some more driving/listening.

Check the A/C compressor pulley bolt is secure, otherwise the compressor possibly has an internal failure.

I was away for a few days, but today I arrived home and was able to drive my car again. I am now sure that the issue is not AC related. The AC works fine if the engine is turned off (with ignition on). I can now also confirm the last part of my initial post, when idling or driving very slowly, the vibration slowly kicks in. This is my first car, and I don't know much about the inner workings of a car, but it seems to me that the issue could be with some part involved in the system that adjusts the RPM of the engine in order to be able to produce enough current.

Your A/C compressor is driven by the engine, so can do nothing to produce any cooling at all when the engine is not running. 

Oh it makes sense, so with the engine turned off, only the blower worked. Still, the vibration kicks in also when I'm not turning the AC on.

Surprisingly, the compressor still operates at a low duty cycle even when A/C is turned off. 

Compressor drive pulley shear plate has let go, one of the now loose drive straps has not yet been thrown radially outwards (will need running at high RPM) so is unbalanced hence the vibration, they normally make a terrible screeching & graunching noise as well but yours might not be touching the inner hub.

1 hour ago, anstj said:

it seems to me that the issue could be with some part involved in the system that adjusts the RPM of the engine in order to be able to produce enough current.

 

Pray tell what system that would be?

3 minutes ago, J.R. said:

 

Pray tell what system that would be?

🤷‍♂️ I don't know, I already mentioned I do not know much about cars, this being my first one (I got it only 6 months ago). 

Thanks for your answer. I'll go for a short drive this evening, to see if I can gather any more useful information about the issue.

Does the aircon blow cold air!, would be the starting point to rule out any faults there.

I found out what is wrong. A part of the right radiator fan is broken/missing. Looks like the right fan starts every time when the AC is on, and obviously when the engine needs cooling (more so when driving slowly with the engine warm). The part in the red rectangle is missing (picture from the web);

 

 

I can't see much without having the radiator fan frame removed, hopefully neither the frame nor the radiator are damaged.

I will definitely go to a service to have the fan replaced, but I was thinking of buying the fan myself. The only thing written on the visible part of the fan is "Siemens VDO" and after some googling I found out it's either VDO A2C59511338 or VDO A2C59511340. Both are physically the same (292.9mm), but the first is rated 150W and the second 200W. Browsing aftermarket parts shops, I see I get options ranging from diameter 290 to 295mm, with power consumption going from 150W to 220W.  If what I'm now having on the car is 293mm and 150W, could I buy a 295mm 200W? Or should the wattage exactly match? I don't expect the 2mm diameter difference to be a problem.

Also, there are quite a few brands available: Topran, Nissens, Autogamma, Mahle, Febi Bilstein, SWAG, NRF, Thermix. The price difference between these is not that big. Is there a brand I should prefer?

Edited 30 June, 20223 yr by anstj