R129 AC problem

[jjrodger]

I have a problem with the AC on my 1999 R129 SL500.

It runs fine in "EC" (Economy) mode, ie without AC. However if I turn the AC on, the air supply dies after about 10 to 15 mins. The fan speed increases (as the in-car sensors detect the increasing interior temperature), but no air comes out of the vents. This happens even if I override the "Auto" setting and turn the fan up to max and demand air from the vents: still no air blows (although the fan speed increases). The problem is temporarily cured by switching back to "EC" mode for a few minutes; the air then blows strong again. However, this means regular fiddling with the aircon controls.

It has been suggested to me the evaporator is icing up, but I don't know what this means or how it might be fixed. Any help would be aprreciated...