1981 300D Fan not kicking in

Weather finally got hot here on L.I.. Had the a/c running pretty much all day. Got stuck in stop and go in the Lincoln Tunnel and noticed that the fan in front of the rad. didn't kick in and the temp gauge went higher than
normal. Cut off the a/c and put it in neutral and it came back down a bit. It didn't overheat though. I am concerned and would appreciate any input as to where to start looking to correct this problem. Someone said there is a 212 switch that sometimes gets stuck. Can't find any reference to it in the Benz factory manuals. Also, the fan spins freely, so I believe its not frozen up. Thanks in advance, George
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again unless it gets over 100C it may not turn on.
its not hurting anything. the HUB CLUTCH fan will LOC but you will not hear it at idle.
let the car idle in your drive way. bring the RPMs to 1,500 when 80C or less let it get to 100C + BRING IT up to 1,500RPM once again. the fluid <clutch> should kick in<give it time> & sound like a prop plane on take off. it will free wheel once again once it cools a bit. the fins on the clutch fan monitors the heat coming from the radiator
the electric fan should kick in at temps a little over 100C.
do not keep your head in line with the spinning fan blades have had 2 break off in as many years.
the case, minus a few cans!
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The 123 body diesel engine will NEVER turn the aux fan on by engine heat. It ONLY works thru the temp sensor on the receiver drier. The engine fan clutch will not lock up if the radiator is plugged and you have poor water flow thru the center. The fan clutch HAS to sense heat to lock up.

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