Fan not turning on

[Chamberpains]

I imagine cutting into the high pressure switch would be another effective way of getting the fan to come on. One way to test if it's going to throw any kind of codes is to Simply unplug it while the engine is running and see if any lights come on.

Just be prepared because most newer trucks tie the air conditioning circuit into cab controllers which throws warning lights and things of that nature. There is also often a minimum run time for the fan when it is engaged for high pressure on the air conditioning. Usually 30 seconds or more or even sometimes it's set to a minimum vehicle speed. So it may not shut off exactly when you command it too because of this time/speed limit.