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Beardedtrucker

So, this could have been covered, but as the title states I have a situation I’ve been curious to know about. I’ve looked and looked online but haven’t really come up with much. So, is it normal for the fan to come on and off every 15 seconds at idle? On for 15 off for 15. At speed nothing unless I’m climbing hills with some good weight in the back. But at idle and under 30 mph it’s just on and off and damn annoying. It just doesn’t seem right. Gauges are reading perfect. Water stays at 170-190. Asking y’all to see if anyone knows exactly or really positive it’s a certain thing or do I need to examine multiple things? Just getting a good idea where to start before I nip it in the bud. Still new to this truck and Cummins in general. Isx15 2350.

Nostalgic

A/C high pressure cycling. If it's every 15 seconds like clockwork, you're either overcharged, or the ambient temp is well over 100.

Beardedtrucker

Ambient temps don’t reach above 90 really in Atlanta. I should mention it starts doing it about 1 min after cranking the truck when it’s cold. Also to note the ac doesn’t blow as cold as it use to after truck is warmed up. Unless im at speed. And also it kind of cycles to blowing cold to a less cold to just air then back to cold…sometimes lol. Like it has moods. Maybe that info is worth a penny with this.

Chamberpains

15 second intervals is also the time it takes for an auto reset breaker to cool and reset. Make sure you don't have any over heating/shorted breakers in the fuse panel. If you find a hot one that is tripping then you have a short in that associated circuit or a weak breaker.

JimT

First glance it sounds AC related. Of course the sure fire way to find out why the fan is running would be to hook up Insite, open data monitor and see what it reports for the engine fan. Takes the guess work out. Once you know why the fan is running then you can focus on the cause.

Mr Hagg

When we have any questions about the fan coming on I hook up to insite and see whats comanding fan on and off. At that point I know what to do to fix problem. The most common problem is the high pressure switch on the ac. It will get loose terminals and as the engine vibrates it will cause it to loose connection. We normally tighten the pins up in the connector with a small pick. I have seen a few cases where the wire was broke at the end of the pig tail from where it was tie strapped over but rare. But really need to hook it up to know for sure,,,

CANNONBALL

Agree see what’s commanding it on. Had a T800 that nothing would fix. Nothing was commanding the fan on. Ended up being the plug on the fan control switch. Only did it sometimes then it wouldn’t for a month.