Hello,


I have a strange problem on my 2003 ML320.


AC used to work fine until recently. Refrigerant charge has been double checked and refilled (pulled vacuum and recharged).


It seems like the compressor does not engage while driving, but will start to blow cold air when stopped at a red light, or coasting to a stop from exiting the highway or something. Once the engine is not at idle RPM, the cold air stops blowing.


I also tested this on the freeway at speed. When traveling around 80 mph, the cold air does not blow, but once I throw the transmission into neutral and let the engine drop to idle, the cold air will begin to blow while I am coasting at highway speeds in neutral.


Any ideas before I start replacing parts? I already got a spare compressor off a 2004 ML350 ready to swap in if necessary.