Groaning noise (possibly AC related?)

[gaza1994]

Right, this could be long winded, bare with me on this one.

So, i've made posts on here a few times about my AC, when it was on, it made some pretty weird groaning noises that changed with the RPM of the car, this got fixed several months ago (it was a bearing inside the AC compressor or something - they replaced the AC unit) all seemed well!

However, now, i get this same noise when im driving (with the AC off) - but the interesting thing is, when i turn the AC on, theres a "thunk" sound (ac compressor engaging) then the groaning noise is gone completely, car sounds normal!

Turn the AC off and its back to square one, it sounds like a horny cat again!

anyone care to shed some light as to what it could possibly be?

[RUM4MO]

The compressor on these cars is engaged/driven at all times, it is a variable displacement type of compressor so when you don't need/want any chilling from it, it is still running but at a very duty cycle - ie just pumping a small volume of compressed refrigerant round the system which is enough to move small amounts of oil around and keep all the "rubber" seals/pipes coated in oil so better able to keep the system almost sealed to the outside world.

So, you should not be hearing a clunk when it engages, all that happens when you demand chilling effort is that a solenoid inside the compressor body presses on a plate to increase the effective pumping volume of that compressor. I seem to remember that the plate gets tilted more to increase its pumping capacity, could be slightly wrong there though, but you get the picture hopefully.

So, when that compressor was replaced, maybe they just used an old one that lasted long enough to get through your warranty - if not, maybe that new compressor has still got some warranty like left in it - did you buy this car from a VW dealer or an independent garage?

Edit:- when you demand chilling, the main radiator cooling fan will be getting switched on - it is not it switching on and off that is causing the change in noise is it?

[gaza1994]

The compressor on these cars is engaged/driven at all times, it is a variable displacement type of compressor so when you don't need/want any chilling from it, it is still running but at a very duty cycle - ie just pumping a small volume of compressed refrigerant round the system which is enough to move small amounts of oil around and keep all the "rubber" seals/pipes coated in oil so better able to keep the system almost sealed to the outside world.

So, you should not be hearing a clunk when it engages, all that happens when you demand chilling effort is that a solenoid inside the compressor body presses on a plate to increase the effective pumping volume of that compressor. I seem to remember that the plate gets tilted more to increase its pumping capacity, could be slightly wrong there though, but you get the picture hopefully.

So, when that compressor was replaced, maybe they just used an old one that lasted long enough to get through your warranty - if not, maybe that new compressor has still got some warranty like left in it - did you buy this car from a VW dealer or an independent garage?

Edit:- when you demand chilling, the main radiator cooling fan will be getting switched on - it is not it switching on and off that is causing the change in noise is it?

I bought the car from a used car place - wasnt a official VW place - so no idea on the parts used.

and like i said above, when its off, i can hear groaning noises that change with the engine RPM, when its on, the car sounds normal..

The "clunk" i think is what ever is stopping the groaning noise, quite a weird one, it doesnt seem to effect the car other than it being noisey.

[RUM4MO]

I'd think with your out of town location, and this cold weather, that you will not have heard your engine coolant cooling fan running at full speed for some time now?

Unless I'm totally wrong here, when your engine heats up to maybe 90C, the cooling fan is switched on at its low speed, if it stops the coolant temperature rising over 95C it will just continue to run until the engine coolant temperature is back down to maybe 85C and then switch off, if it does not stop the engine coolant temperature rising, when the temperature hits 105C roughly, the fan speed will get switched to full speed and continue at that until the engine coolant temperature is pulled back down to roughly 100C then dropping back down to slow speed etc etc. When you switch on the AC and request chilling, that fan should be getting switched on at full speed regardless of engine temperature.

One thing to check in that area, with the engine cold and not running and with ignition still off, open the bonnet and spin the cooling fan with your fingers - then listen to if it sounds rough or not. If it sounds rough, then probably your cooling fan is about to fail due to dried out bearings - just a though and something for you to check.

Edit:- remember, or in case you did not know this, if your car has an engine temperature gauge, and the 1.4 might not, while that display is an analogue one, ie looking like it can display an infinitely varying range of temperature values which might leave you thinking that it can discriminate changes of 0.5C, in reality it is being supplied with temperature information from a digital source, which translates into "90C" can be any temperature value between maybe 80C and 100C etc etc.

[iichel]

here you can see how skewed the temperature gauge actually is.
93C to 125C will show as 90C on the indicator

horizontal axis -> how much rotation in degrees
vertical axis -> temperature

[gaza1994]

so - do we think its the fan at the front of the car causing weird noises? i'll go stick my fingers in and give it a whirl to see if it sounds weird later this afternoon after work (i need my fingers for my job aha!)

EDIT: i dont have a temprature gauge either, so i'll need to plug in VCDS / OBD2 thingie to get any kind of info out of it