I believe that what is happening on yours is that the evaporator is being covered with ice! I have seen this before when the drains are blocked or when the evap temp sensor is faulty and not cycling the compressor. If the sensor on the rear of the compressor fails, it will not come back on until you turn the key off and back on again.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM