1999 ML320 ongoing AC problem
 

I have had an ongoing problem with the air conditioning not turning on. The cabin fan blows normally, but it appears that the compressor doesn't always kick in. When it does, it cools fine. I've had mechanics work on it with no success. I've blown a fuse a few times, and the dealer replaced it with a 40 amp because of a service bulletin. I've had the electric fan clutch replaced supposedly because it was very weak and may not be removing the heat properly. I've also had the control module inside the cabin replaced, again with no success. A knowledgeable friend of mine thinks that I have a ground wire loose, which may be causing my intermittent problem. Has anybody already seen and conquered this problem?

We have had some "trucks" with intermittant A/C operation that was caused by the pressure switch on the high pressure line.
Also the wiring connectors under the fuse box might not be making a good connection.

MB Doc
 

I have the same problem with my wifes 98 ML...the compressor will cut out with no warning, and then it will start again sometimes minutes, sometimes days later....how do I check the pressure line you were talking about in your post? My mechanic had been able to bypass and get the compressor going, but is there something in particular I need to have him check? The A/C compressor works great when it can be persuaded to work....blows out ice cubes.

AC Intermittent
 

My 98 ML320 has intermittent ac also. The #44 fuse is fine and the refrigerant is OK too. At static, it reads 100psi and with the compressor running about 30 on the low side and 325 on the high side. All in the normal range for a 90 deg temp.

The compressor may not engage for several days then oddly starts working again. When the compressor kicks in the aux fans work great and it blows 38 deg air in 90 deg temps.

I'm baffled by this. I tread a visit to the MB dealer but it's beginning to look like I can't avoid it. I've taken it to an indie ac tech and all checks out fine. He recommended the dealer next. Says the AAM is not directing the compressor to turn on.

Does the AAM control the compressor in the 98 ML? Anyone have any ideas other than taking it to the dealer? TIA.