Engine fan on, coolant temp low.

X2

 

I do have a switch on the dash for the fan, it’s in the AUTO position. The fan is on with or without A/C on.

I see two pressure switches by the EVAP valve, both are labeled A/C HP Switch. I have another pressure switch on the SMALL Line coming out of the A/C Compressor, this one is labeled A/C Pressure Switch…which one controls the fan?

 

Build up air, shut the engine off, turn the key to the on position (make sure the a/c is off and engine temp is low enough that the fan won't be locked), try to spin the fan by hand. If you can't turn it your fan clutch is worn out.

 

Thanks mudflap77

The fan turns fine!

 

You're welcome. Next step is connect cummins insite and see what is calling for the fan..

 

Man, i was hoping to avoid the expense of a diag charge from Peterbilt.

 

I wouldn't take it to Peterbilt. I would go to a local independent with a proper scan tool or Cummins Insite and ask them to diagnose it.

 

Wasn’t on a Cummins, but I had an intake air temp sensor go bad on a Cat and it caused the fan to run constant.

 

Try unplugging those AC high pressure sensors you found first and see if one of them makes the fan turn off. You may need to stop the engine and unplug it, then start it up. Worth a try, though I don't know if those are normally-closed or normally-open switches. The other thing that will make the fan come on is the coolant temperature sensor.