Your Mercedes vehicle will flash a host of service lights to inform you when something might be damaged inside the car. If the air conditioner unit is not running normally or is only blowing out warm air, it may be a temporary fault. Sometimes the unit isn't actually damaged, and resetting your climate control unit will allow your air conditioner to work as it did before. Be aware that if you reset the unit and it again stops working, you need to take the vehicle in to the dealership for repairs.
Insert the key into the Mercedes ignition and turn the ignition cylinder to the "2" position. This is as far as the cylinder will go without cranking the engine.
Press and hold the defrost and recirculated air buttons simultaneously. The defrost button has three lines going through it, while the recirculated air button has a picture of a car with a curved line through it. Hold these buttons down for about five to 10 seconds, or until the LED lights on both buttons start flashing.
Wait 45 to 60 seconds for the LED lights to stop flashing. Then turn off the car.
Wait 60 seconds and then start the car engine again.