My A/C stopped working on my 97 E300D. The Red "EC" Light stays on which I assume is the compressor economy Mode. What tests or assumptions can I make thus far. Will the Light go on if the refrigerant is low to protect the Compressor?

I located rebuilt Compressors for this car for $430, yet if it's just a leak I would rather not replace it.

Any advise would be greatly appreciated.