W107 Auxilary Fan Operation
Submitted by Don Wilson on 01-28-2012
The auxiliary electric fan on our 1975 450SL comes on when the engine is first started cold. Once the engine is up to temp the fan shuts down and I have yet to see it come on once the engine is warmed up to operating temp. The engine runs at about 175-180F steady state so possibly the sensor (new) is not turning on the fan. I'm curious as to why the auxiliary fan comes on when the engine is cold. Is this correct or do I have a potential problem?
Comments, suggestions welcome. Don W.
The aux fan should only come on when temps exceed 105C or when the high side pressure switch reads something north of 350lbs on the high side.
I'd check the temp switch for the aux fans...I'm not 100% if the early switch is resistance based or an on/off affair. Checking it w/ a volt/ohm meter should tell you, I'd leave the leads hooked up and see what changes as the car warms up. You could also try unplugging the high pressure switch leads, see if the fan still kicks.
Let me know what you find and we can take it from there!
Jonathan
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