I have a 92 W140 with the stright six M104 engine, a 300SE.

When the car is cold, I fire it up with the air-con "ON", it will make some hessing noise for about two minutes. It sounds like sliping belt or something.

When the car is cold, I fire it up with the air-con "OFF", it will not make the sound at all.

When the car is warm/hot, its normal with no special noise. This also applies to starting from a hot engine with air-con "ON".

So guys, what is it? The compressor about to go? or something less expensive? Should I be worried? Should I get it looked at?

Any advice will be appreciated. Actually other than the above, everything is working fine, well at least to my understanding.

Thanks