How to Reset a Mercedes AC System

1. 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.
2. 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.
3. Wait 45 to 60 seconds for the LED lights to stop flashing. Then turn off the car.
4. Wait 60 seconds and then start the car engine again.