AC Making Noise When On

[unknown99]

I noticed that when I turn on the AC you hear this knocking then when you turn it off it goes away. What could this be? I have a 09 Corolla. https://streamable.com/ovgqfd

UPDATE:

when the ac button is turned on you can hear it from the engine. I opened the hood and hear the noise coming from maybe the alternator/

 

 

 

[oldcodger]

Hi,

Could be one of several problems.  first is the belt in good condition ?

It may be  the Aircons Compressors Clutch making the noise or the the Compressor itself.

Other possible things could be that when the compressor is activated its putting extra load onto the belt thats affecting the other devices it drives including the ider wheels and the tensioner mechanism.

You can usually check most parts by removing the belt and then rotating them by hand to see if they are noisy or have a lot of play in their bearings.

Also check the actual crackshaft pulley is sound and secure.

[Red_Corolla]

I fear it might be the compressor itself, judging by the cadence of the noise. Probably need to remove the wheelarch liner and go in with the mechanics stethoscope (aka long screwdriver) for further diagnosis.