Have you checked to see if anyone has intentionally bypassed the aux fan preresistor behind the left headlight? I read a post about people permanently bypassing the resistor to get high fans right away in hotter climates. The high fans would then be activated by the pressure switch on the receiver dryer. If your pressure in the receiver was still low, the fans would not come on right away after you started the engine. Also, I think a normal operation would be for the low fans to come on (or if the preresistor was bypassed--the high fans), then, when the pressure in the receiver dropped back down, the fans would shut off--all this taking place below the trip point for the coolant temp (105-107C) that would normally set off the high fans.

Check out Author Dalton's reply to GregS back in 2003.

http://www.peachparts.com/shopforum/showthread.php?t=67682&highlight=aux+fan+resistor+bypass

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles