I have yet to see the aux fan run. In hopes of tracking this

A) Is the cable emanating from between the two fans the power cable?
B) Are they supposed to run when the A/C is on?
C) What Temp should they come on at?
D) Where is the relay(s) for the above?

The aux fans are designed to run only when the engine is over heating or the a/c pressure is high enough to turn the switch on. There are different pressures that the a/c switch can operate to turn the fans on.
The fans run at a lower speed with the a/c than engine overheating.

A quick way to check this is to bridge the high pressure leads at the drier for the A-C. The switch will be green or red. Just take the 2 wires loose and bridge them and the fan should run on low.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Both fans run when the switch is jumped so they work. Putting the system to auto didn't make them come on. Is the pressure occasionally high enough to operate the fans on low speed?

Also what temp should the coolant reach before the fans run at high? I have seen as high as 100C. I would think it would be closer to the operating of about 90C.

The coolant temp switch that controls the aux fans for overheating is a (blue) 2-pole switch in the cylinder head. It sends a varible resistance to the a/c pushbutton & it turns on the hi-speed fan relay, overheating is considered above 107C.

Apparently I am concerned for no reason. Thanks for the help.

Chris

One last item, is the high temp switch behind the injector pump? Or further back?