Thank you Arthur--I'll try that to see if I can get the thing to ice up again.

I wanted to check system pressures with windows down, doors closed, max cool and max blower because those are the conditions on which the chart in the service manual is based. From this test, I think I've ruled out over serviced refrigerant

I have since bought a vent temp gauge, I'll leave it stuck in the vent over the next few days. If I notice temps below 40F just prior to the loss of cooling, I'll know the system is icing up. If and when that happens, I'll jumpout and see if the compressor is still engaged. Maybe I can figure out what's happening.......

Stay tuned

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