12.7 60Series Fan always on 1998 INT-9400

Well, I had a similar thing with my n14 after I bought it. For few months I was pulling my hair trying to figure out why was the fan always running, ended up ECM was programmed for manual switch, but truck did not have one.

 

If you have a Horton fan you need a normally open solenoid, Kysor fan needs normally closed. With the key on, you should have constant power at the red wire at the solenoid. The ECM will control the ground. When the solenoid is on(energized), the fan should be off(disengaged). So when the solenoid is unplugged, the fan should be on, (engaged).

 

They are supposed to have fail safes so that if you have no air, fan is engaged. Or, broken wire, fan is engaged. So yes, you have something quite wrong there. The AC pressure switch for a Detroit is a separate input to the ECM and it will turn on the fan depending the state of the ac pressure switch.

 

I was having similar issue on my Detroit 12.7 with a Horton this summer. Replaced solenoid, AC switches, checked AC pressures, manual switch… ended up replacing the fan clutch and it fixed it.

How does your fan clutch look? Rusty, dirty? Some say you can blow it out with air or lube with some PB blaster and it fixes it. New clutch fixed my issue.

 

Here is the link to my thread if it helps.
96 FLD 120 / 12.7 S60 Fan Always On

 

I just spray it with brake clean and blow it off with shop air.