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Wondering what controls the speed of the cooling fan on the Hemi. From what I'm reading it's not an electric fan like the 3.7 and 4.7. The high speed on the fan does not come on early enough and my head pressure for my A/C gets too high.
 

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Wondering what controls the speed of the cooling fan on the Hemi. From what I'm reading it's not an electric fan like the 3.7 and 4.7. The high speed on the fan does not come on early enough and my head pressure for my A/C gets too high.
I'm wondering the same thing if anybody knows. My mother's Commander has good AC while it's moving but when it's at idle it's very hot. It seems to be a cooling fan issue and the fan does not speed up when turning the air conditioner on.
 

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The Hemi Hydraulic Fan is driven by the Power Steering system, I suspect that is why the Commander stipulates a special hybrid Hydraulic/Power Steering fluid MS-10838 for the Power Steering.


So if you have a Hemi, definitely do NOT use some other PS fluid, get the correct MS-10838 fluid from the Dealer.


A hydro/electrical/mechanical switch likely controls the fan speed, the computer triggers a solenoid valve in the hydraulic fan to let more pressure into it to turn faster.


Obviously, as the hydraulic motor wears it will be less efficient at converting pressure into motion, just like when a pump wears it makes less pressure for the amount it turns, and the hydraulic motor is a pump in reverse and don't forget you need power from the PS pump that is working harder and wearing faster with the hydraulic driven fan.


Also, don't assume fans are the problem for AC, yes, they very well could be, but also having a slow leak and be low on refrigerant will cause the AC too cool less and it will be worse at a stop than moving.
 
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