1997 Other Mercedes Benz Models Climate Control

This is not a failed control unit. The EC light comes on and stays on when there is no frion in the AC system. You have an AC leak somewhere causing this. This is also why you are only getting hot air because there is no frion in the AC system.

Sorry for the delay the notification for your last response must have been missed in my email. If you have a fully charged system and the EC is still flashing I would verify that the compressor clutch is engaging on the AC compressor unit. Run the motor and have a friend sit in the vehicle. With the AC off identify the compressor and have your friend turn on the ac while you are looking at the compressor. The front of the compressor clutch will engage and start spinning with the AC compressor pulley if the compressor is operating correctly. If this does not engage then your compressor clutch has failed and the compressor will need to be replaced.

Okay so you say you have no leak and the ec light is still flashing. I am interested to know the pressures that are being read on the high and low side of the system. Are you able to check these values? From my experience the EC flashing is almost always related to low pressure in the system. I am wondering if perhaps you are getting incorrect pressures on one of the side causing this to activate. Please let me know if you can acquire the high and low side pressure values. Also was the system checked for leaks when it was recharged? Did they let the AC system sit in a vacuum pressure for any length of time to check this?