4.7 Hydraulic cooling fan manual switch - North American Grand Cherokee Association
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Old 05-08-2019, 12:48 PM   #1
Moose Magnet
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Default 4.7 Hydraulic cooling fan manual switch

I want a switch to force the hydraulic cooling fan to spin. Has anyone done this?
I believe the fan comes on too late, when the temp it too hot. It should come on sooner.
New: water pump, radiator, hoses, thermostat, coolant and flush.
The fan has come on only once when the water pump gasket failed the engine overheated. Seems it came on late. Should come on BEFORE it overheats.
Anyone devise a manual switch for the hydraulic fan?
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Old 09-01-2019, 09:36 PM   #2
Oldbeginner#63
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HYDRAULIC FAN STRATEGY
The hydraulic radiator cooling fan is controlled by the FCM. A PWM (Pulse Width Modulation) signal from the JTEC controls the fan speed. There are four inputs to the FCM that determine what speed percentage of fan is required by the vehicle. These inputs are:

Engine Coolant Temperature
Transmission Oil Temperature
A/C System Pressure
By monitoring these three parameters, the FCM can determine if cooling airflow is required. If airflow is required, the FCM will slowly ramp up (speed up) the fan speed until the parameter(s) are under control. Once the temperature or pressure is reduced to within operating parameters the fan will ramp up, ramp down, or hold its speed to maintain the temperature / pressure requirements.

If you haven't put in the manual switch yet you might try to assess which of the 4 input sensors listed above is bad.

Last edited by Oldbeginner#63; 09-01-2019 at 09:40 PM.
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Old 09-01-2019, 09:40 PM   #3
Moose Magnet
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Nope. Won't try any manual switch. I've learned that it's designed/engineered to run hot. To run at 210 or above. I don't like it. But that's they way it is. Junk engineering.
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