E-Star

Since a few weeks there is a strange noise from the AC system, probably from the AC compressor. Until now, it only occurs if the car has been driven with AC off and stands for about half an hour.

The noise occurs approximately every 10-25 seconds. When I start the engine and turn it off again, the noise is gone for a few days.

The compressor has been replaced with a new one 7 weeks ago. The noise sounds to me like pressure is released, maybe from the high pressure part through the compressor to the low pressure part of the AC system.

I monitored the signal of the pressure sensor via SD, slowly decreasing after turning off the engine, but no remarkable change in pressure when the noise happens.

Cooling works flawlessly, no sign of any leak.

Did anyone had a problem like this before?

ygmn

If that is from AC system it doesnot sound normal nor does it sound good.

You are talking about that SCREECH? cannot be good

Man it hurts my ears like nails on chalkboard.

I would go back to whomever replaced compressor as it could be compressor clutch or not enough compressor oil?

thefisch

I've heard and seen pressure release from an AC system and it was much louder than that - reminded me of a steam whistle. Also, there is normally evidence of a purge near the pressure release valve - you can see the oily residue. Have you found that?

With that said, that sound you posted is not normal and I agree with ygmn that you should bring it check for them to check. At least they will note the noise in case it fails on you later on.

E-Star

I already removed the bottom cover. There are no signs of any leak - everything is clean. New shiny compressor. Also no evidence of a leak at the top of the compressor where the hoses are attached. I assume it originates internally.

I'll take it back to the workshop (official MB, by the way). The only problem is that reproducing the sound is a quite difficult. At least, I have video evidence.