Do you guys notice any change in the sound from the engine bay when you turn the a/c compressor on? When sitting in the car with windows closed, I noticed some sort of knocking noise from the engine bay when I turn on my a/c compressor, which disappears when I turn the a/c compressor off. However, I cannot notice any noise when I stand in front of the engine with the hood open. What could be the problem?

 

I uploaded a video for my problem. Please use earphones or turn up volume to hear the noise.

 

My LS400 made a rumbling noise when I turned the AC on. AC still worked but it was a compressor failure. I could definitely hear it from the front of the car though.

 

bbtri did you solve your problem? How did you fix it?

 

Old compressors will make noise, replacement may be needed to stop that. Have the system checked to see if there are any inconsistencies in the pressure indicating an internal issue starting to happen.

 

The bearing in your air conditioner compressor clutch may be worn.

Remover compressor clutch and replaced bearing on my LS400:

Here is post:

https://www.clublexus.com/forums/ls-...lutch-p-n.html

The main thing is to mind any staking of bearing on clutch pulley - these stakes must be removed before pressing out old bearing or you will ruin the pulley.

 

I replaced the compressor. It had no oil in it but the rest of the system did. It must have been blocked somehow. If I had known I would have tried adding a few ounces of oil to the compressor to see if it would quiet down.

 

Some people in the Youtube comment section suggested that it is normal for variable displacement piston compressors to make such noise if the refrigerant level is too low. Will have an indy mechanic check my car tomorrow to pinpoint the problem.