The fan would need to be connected to a temperature sensor in order to know when to turn on. Some of the conversion kits include these.
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1999 Blazer 4x4 LS "Blackie"
Monroe Reflex Shocks
Moog U/L Ball Joints
K&N FIPK Gen 2 Cold Air Intake
Flo-pro Soundpro exhaust
Optima Redtop
132k miles and still rolling....