EC= economy mode, no compressor operation.

On that car 7 MOST newer MB's that can mean almost anything.
The A/C controller doesn't turn the compressor directly. IT sends a signal to another control unit called a SAM (signal activation module) & that module looks at the refrigerant pressure & temp & then turns on the compressor.

To diagnosis a MB scanner is needed to see what command signals are there & what pressure is in the system.

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