2002 ML320 - The ac is not blowing cold air

I just had the same prob. Your air blend door actuator has probably gone bad. Take off the glove box and look 4 a little black plastic box(oddly shaped)with white plastic arms connected to it. Turn the knob from heat to cold. If those arms dont move thats your problem. Or when u turn the knob, u hear a clickig noise inside the dash, thats also the air door actuator.

This could be from many reasons,, the simplest is to have leak from the expansion valve , low gas ,, == hot air
could be also from the condenser <leak>
could be from dryer <leaks>
The worst is to have deffective compressor ,,, very expensive repair

You could be just low on freon. The cost differs to where you go. Unfortunately Air conditioner systems are complicated and require trained professionals. If it is as simple as just adding a can of freon then it is not very exspensive and you can do it yourself for around $15.00 for the hose and a can of freon but that is only if your compressor is operational. If you have someone stand outside and watch your AC compressor while you cycle the switch off and on he or she should be able to hear the clutch engauge. If it engauges then you are probably just low and can get away with adding a little at a time until you get cold air our of your vents. The temperature out your vets should be in the range of around 20 to 30 degrees below ambient temperature. If it still does not work the you need to take it to a trained professional. Did you check your fuses as well?