wrooper, If I recall correctly, your vintage 124 uses a pressure switch to activate the aux fan low speed at 20 bar pressure, and to turn off at 15 bar. Doing the math in my head, 20 bar is somewhere north of 290 psi. That is, if your pressure switch has a red base. If green, the corresponding specs are 16 bar/12 bar.

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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