Mercedes: climate control stuck in EC, freon 12, better mileage

Question
Cannot turn off EC and A/C will not blow cold air. EC turns off only when using defog for windshield.

Answer
Chris
I have researched your issue and find that the (EC) Economy button is designed to disconnect the Air conditioning compressor for better mileage. When the AC develops a fault then the EC light stays on.
I would find an independent Air Conditioning service and have the freon checked. When there is a pressure problem with the AC, there should be a code tripped in the car computer. This code needs to be read by a scanner, the independent service should have a scanner. Check before you decide on allowing them to do the job.
Various components in the AC system can fail, compressor, hose connections etc.
It is vital that you have these components repaired before refrigerant is recharged. It is expensive to have the freon 12 or 134A just escape.
In fact it is required by law that the 12 not be release into the air because of Ozone depletion.
A good repair center will be able to inject a refrigerant with die that can be see at the site of the leak if it under the hood. If the evaporator under the dash has developed a leak, it will require a freon sniffer to determine if the leak is there. If so, be prepared for an expensive replacement, as it usually requires complete or partial dash removal to replace the evaporator.
Good Luck and let us know how thing go.
Rob