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my fan come on when air compressor come on how can i stop this 2016 prostar cummis meed help bad fuel milage
There is no "air-compressor" sensor in the engine as far as i know of to make the engine fan activate.


If your air pressure is dropping below 90-psi, then the engine fan will kick on (along with other things happening sometimes) because the air system is trying to protect itself from locking up the brakes (due to low air pressure) and half the air-related systems will shut down / switch off to conserve air pressure.

maybe a bad air-dryer unit allowing air to drop below 90-psi before the compressor kicks in?.. maybe bad/stuck governor inside compressor?

aside from that ...
Look in Insite to see why the fan is coming on. It is likely due to A/C and not air compressor if it is not a low-air pressure issue on the truck.
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