Have Mercedes Questions? Ask a Mechanic for Answers ASAP
Hi, if the blower motor is running the air flow is probably blowing up through the defroster vents. If that is the case the problem is caused by a vacuum leak in the vent system. The vents are opened and closed by vacuum. When a leak develops in the system the air will default to the defrost mode.
Let me know if you have any questions. Please rate my service in order for the website to credit me for taking your question.