Thank you all.

I will check refrigerant charge and post it here.
I also would like to check the compressor fuse. Could you please tell me where it is located exactly. Is it in the Fuse box.
the loose connection referred to by lenny, is this connection at the blower.

I believe the problem has something to do with the heat.
Only when the car is sitting under the sun for some time the problem shows.
It does not appear when I start from the garage in the morning.

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300CE 1989 Euro Model.
ML350 2011.