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.Google+
Car Problem Reports
Mercedes-Benz ML500 AC System Leaks/Bad Temperature Sensors May Cause Poor Cooling
Mercedes-Benz ML500 Problem
Average Mileage: 126,846 mi (82,102 mi - 193,000 mi)
Visitor, 2002 Mercedes-Benz ML500, 83,000 mi
When i am turning on AC in my car radiator fan is working on high speed, and i have no cold air. I changed auxiliary water pump & i still have the same problem.I have full freon in system. Thank you.
Visitor, 2005 Mercedes-Benz ML500
the AC blows out warm air..sometimes works though...when it 1st started happening, it seemed like if I rolled the window down the AC would start working..
Visitor, 2002 Mercedes-Benz ML500, 166,000 mi
When Idling the A/C slowly begins to produce warm air. When accelerating and driving in traffic or on the highway the A/C works very well.
Compressor turning but no cooling. Freon level is low but not at a point to stop compressor.
Visitor, 2006 Mercedes-Benz ML500, 82,102 mi
ac was blowing and all of a sudden it just stopped.
Visitor, 2005 Mercedes-Benz ML500, 110,130 mi
Ac was working fine while driveing all in a sudden hot air was blowing out then after several ignition turn on and off the ax starts working good again then goes back to the same problem cycle over and over note this problem was not repaired.