Update:

I've been driving around with a thermometer stuck in the vent since my last post. Finally today, an observable fault occured. Ambient temp in the mid 70s so AC not really needed. Selected EC mode but noticed air coming from vents about 40F. Checked under hood, sure enough, compressor engaged. Tried turning system to O--compressor still engaged. Maybe magnetic clutch not disengaging properly. Disconnect three pin connector from compressor and compressor disengages. Check schematic--three pin connector leads to N6 (A/C compressor control) Find N6 location from service CD, swap N6 with unit from my other car and now operation normal. Other car compressor operation faulty with suspect N6.

N6 part number is 003 545 56 05, referred to as compressor relay on peachparts and allparts express.

A non disengaging compressor would explain evap icing. Anybody else experienced failure of this part?

J. M. van Swaay

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1994 E320 Wagon, 230,000 miles
1995 E320 Sedan, 106,000 miles
1994 E500 Sedan, 79,000 miles