wrooper, I'm not the AC expert, so I'll pass, though it does seem as though the pressures are low. No, the aux fans do not automatically engage when AC is running. That's under the control of a high pressure switch that monitors condenser pressure. If you're certain that the aux fans do not engage with AC, that might well be another indicator of low refrigerant charge, inasmuch as the charge may be inadequate to build up enough pressure to trigger the pressure switch. What strikes me about your comments is that you say that the temp gauge on the instrument panel shows 80C, but you say that only high temp causes your aux fans to engage. The temp sensor should be triggering aux fans right around 105C (unless it's been significantly modified). Could be the instrument gauge sensor is faulty, still showing 80C with the aux fans running.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't