what make the ec light stay on

EC button on your ac and heating control is to bring outside air only into your car. when that mode is selected, a/c will not come on. You must use other buttons along with lowering the temprature setting selector for the a/c to kick in.

Your EC light stays on with inop AC only when it records a fault in system.Being low on freon will cause this, must erase codes even after freon level corrected.If freon level ok, evaporator temp sensor sill short,send false signal to computer,causeing shutdown of comprssor

so this is all in the coding b ut how do you fix it?

I have a 2002 Mercedes-Benz 430 and my air conditioning cut off leaving my economy light on

No answer