I do not know how to give you a quantity of air, but the vacuum elements that open and close the doors in the heat exchange box do fail often. In fact I have the box out of a 126 now for repair and found two faulty. The only problem is that the dash isn't easy to take off!!

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