My 1997 E420 EC button is on. I had the R134a checked and it is at 90%. What could cause this?

 

run the on-board diagnostics first and log the readouts. the EC/light is a protection
device which prevents burnout of the system. so don't try to fix the light. fix
the cause of the light staying on.

 

+1

Also, you might check for error codes B1233 and/or B1234 which are for the refrigerant temp/pressure sensor. Early model sensors were prone to moisture contamination causing the EC light to come one. A sensor with a better design was made available as a replacement.

 

Thanks for answering. I took it to a local importshop. The system has two very slow leaks. One in the compressor and the other one is at the low pressure port.

 

OK so the light is on indicating the compressor is off (protection as mentioned). Fix the leaks, evacuate and refill the system and the problem is solved.