Compressor issue??

Separate the tractor air lines from the trailer and see what happens. Build the air to 120 and then turn the truck off and walk around and listen. If it goes to 120 and then drops to 103 the air is going somewhere, maybe a slow leak in a tire. Assuming the gauge is correct. What model air dryer do you have?

Bing Videos Very short video shows how to turn off the auto inflation air. You can try this and see if anything changes.

 

Air drier or leveling valves are the first things to look at. Both can be problematic. If the truck is sitting still and it holds, most likely the leveling valves.

The auto inflator system may also have a leak in the system. The light should come on for a minute or two when first starting the truck, that’s when it runs the self test. Unless you have a low tire or a leak, it should not come on after that.

 

My first tbought would be a leaking tire, or lealing thru tee on the auto inflation. You're losing air, the light randomnly comes on, etc.

Couple of symptoms that make a plausible guess.

But it sounds like your compressor is doing exactly what the governor is telling it to.

The constant cycle is from a leak

 

If your trailer inflating system has high/low regulators, it may feels like your 'high' regulator is bad or faulty dump valve keeps dumping air until 103psi where 'low' air regulator kicks in to stop the dumping.