Galley refrigerator not cooling

Slavko Despotovic

Coming back to the boat I find refrigerator not cooling. I can hear fun running and compressor as well. But the plate not cold.
I do not have any instructions on board for the refrigerator. On my previous boat this was a signal that gas has to be filled i. What kind of the gas is on 1999 models of SM? How difficult is to get to the  compressor to fill the gas. Or maybe is the thermostat. How can I test that one?
Thank you for help.
SM 2000

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