The aux fan should come on for two reasons.
1. the pressure of the A.C. refrigerant will get too a high level and it will come on via the switch on the drier bottle (red)
2. The temp switch (green 3 pole) will sense too high engine temp and send it on.
We have the service CD for the 124 in stock.
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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM