AC system leaks and/or a faulty evaporator temperature sensor can cause poor AC cooling. The failed sensor can prevent the AC compressor from coming on. Leaks cause a low refrigerant level, which reduces the ability to cool.
Car Problem Reports
Mercedes-Benz ML430 AC System Leaks/Bad Temperature Sensors May Cause Poor Cooling
Mercedes-Benz ML430 Problem
Average Mileage: 128,500 mi (110,000 mi - 147,000 mi)