Mercedes Viano Diesel AC Issues Resolved

That sounds frustrating. Low voltage could stem from several causes. Have you checked the belt tensioner to ensure the belt driving the A/C compressor is tight? A loose belt can prevent the compressor from engaging, potentially triggering a low voltage error if the compressor isn't spinning correctly. Also, is the pressure sensor properly connected? It acts like a safety switch; if it detects insufficient pressure, it won't allow the A/C compressor to operate.

Those are good points about the belt tensioner and pressure sensor. How should I check the pressure sensor connection? Is there a specific reading I should look for, or is it more of a visual check?

I'm unsure about specific pressure sensor values. However, checking the connection involves visually inspecting for corrosion or loose wires. If the basics appear okay, and given the error code indicates low voltage, it might be wise to consult a workshop. They possess the necessary tools for a more precise diagnosis of the A/C and HVAC systems. This could save time and money in the long run.

Thanks for the advice. I took it to a workshop. A faulty wire was causing undervoltage to the A/C compressor. They traced and repaired the connection. It cost 240€, but the A/C works perfectly now.