Radiator fan randomly going on

Is your a/c on or are you using your defroster?

 

Fan solenoid is failing and eventually your fan will just stay on.
When I did mine it was relatively cheap and easy to do yourself.

 

On my freightliner the Parksmart system causes it to go on. If I leave heat on low fan speed max heat it doesn’t cause the fan to randomly come on for no reason. In summer it’s never a issue only winter/springtime for some reason.

 

Possibly intake air temp sensor too.

 

Wiggle and pull test the wiring at the fan solenoid on the firewall driver side. Pins can get spread and copper can also break inside the insulation.

I agree sometimes replacing the solenoid and just repinning the connector would be a good place to start.

 

@Goodysnap beat me to it. That gods #### solenoid is crap and the connector is worse. I had 3 go out on my 579 and it usually took the air temp sensor with it. Id start there and just have the connector replaced. It costs more but the repins never lasted more then a month or two before it went back in when they failed.

 

If you turn your AC on and the radiator fan comes on what does it mean?

 

It means the high side AC pressure has met conditions for cooling needed across the condenser and is part of normal AC operation.