Engine fan starts without any reason dd15

I always drive with the AC comp off unless I need it for something, whenever I turn the AC comp on or use the defrost the fan always comes on automatically even if it's bls cold outside, 2017 DD13 Cascadia Evo

 

Parksmart system caused my 2015 to kick fan on in winter . That truck annoyed me until I started shutting rear fan off . Then it was normal until it got really cold and I needed to use bunk heat again.

 

your A/C is automatically on when you have defrost on so that the air going onto the windshield is dehumidified. The A/C also controls the fan to keep pressures down in the compressor.
When parked and running move the heater control to vent or floor to stop cycling the fan by the A/C system.
If you are using a winter-front open it up a bit more while moving and close up when parked.

 

Maybe a dumb question, but do you look at your air gauges when it comes on? My engine fan will automatically come on when air pressure is below 90psi until it gets to 100 again.