Car is 2013 Skoda Octavia Mk3 1.4 TSI (CHPA), manual, 118k km driven.

Today I noticed an A/C-related droning/humming noise that seems louder than before, but I'm having trouble pinpointing the source.

Symptoms:

• Only occurs when A/C is on.

• Noise stops immediately when I press the A/C button off (cabin fan still on),

• Most noticeable at idle and especially after revving the engine and letting RPM drop back to idle.

• Above roughly 1500 rpm I can't really hear it.

• Cooling performance is excellent. The cabin cools down very quickly even after sitting in the sun.

• No warning lights or other symptoms.

What confuses me:

• From inside the cabin the noise can be quite noticeable and sounds a bit like a old hydraulic power steering pump, but quieter.

• Under the hood I can't hear any obvious compressor growling, grinding, or abnormal noises. Mostly just normal TSI injector ticking.

• The radiator/condenser fan runs when the A/C is on and stops when the A/C is turned off, but the RPM-dependent nature of the noise makes me unsure whether the fan alone could be responsible.

The A/C system was serviced/recharged last autumn.

Has anyone experienced something similar? Does this sound more like normal A/C load/cabin resonance, a belt/tensioner issue, fan resonance, or an early sign of compressor trouble?

Thanks.

And the car has the automatic climatronic (dual zone) AC.

Mine is the same year as yours, but my fan certainly does not run all the time the a/c is on.

Take the fuse for the fan out or unplug the fan and see if there is any difference in sound.

14 hours ago, Santtumh said:

1. Only occurs when A/C is on.

2. Noise stops immediately when I press the A/C button off (cabin fan still on),

Sounds like the noise of the AC compressor working.

If it cools fine and the noise isn't that loud under the bonnet, Id probably just go on living my life and let the compressor work away as it should.

My suggestion would be to have someone cycle the AC while you listen under the bonnet if you are really worried, but other than tinkering with the AC compressor its probably a leave it alone kind of thing

22 hours ago, ords said:

Mine is the same year as yours, but my fan certainly does not run all the time the a/c is on.

Take the fuse for the fan out or unplug the fan and see if there is any difference in sound.

My best guess is that the radiator fan was running continuously because the AC was on and the cooling demand was high. It was relatively warm outside, around 22°C, and the car had been sitting in direct sun, so the cabin and condenser heat load were probably elevated.

The radiator fan itself does not seem abnormal mechanically. I don't hear any noticeable noise from it, it spins freely by hand, and there is no detectable axial or side-to-side play.

9 hours ago, BlueWagon said:

Sounds like the noise of the AC compressor working.

If it cools fine and the noise isn't that loud under the bonnet, Id probably just go on living my life and let the compressor work away as it should.

My suggestion would be to have someone cycle the AC while you listen under the bonnet if you are really worried, but other than tinkering with the AC compressor its probably a leave it alone kind of thing

The cooling performance is excellent, even after the car has been baking in the sun for hours. This is my first summer with the car; I bought it in December, and winters are freezing where I live, so I haven’t had much warm-weather experience with it yet.

My only concern is that the droning can get quite loud at times. It sounds worrying because I’ve never had a car whose AC makes this kind of noise. Could this be an early sign that the compressor is on its way out? “Luckily,” they typically make themselves known before they grenade.

On 04/06/2026 at 19:45, Santtumh said:

Could this be an early sign that the compressor is on its way out?

Maybe...but what are you going to do about it? Probably wait until it either dies or starts really making a song.

Id just be aware of it and monitor it.

My Landcruiser one makes a fiar noise and I know its gonna die some day....but probably just let it run on until it stops working