Our coach cuts out at 120psi and back in at about 90 to 100psi.
If yours is staying at 100 maybe your cut in/out are set to close together.
Upon start up pressure should build to about 120psi in a few minutes. Then you should hear a good release of air followed by a short slight hiss then it should stop until you use your air brakes or use air some other way (air ride adjustment, air horns, or a leak :E) as it goes down to your cut in pressure the governor should start it building pressure again. This is a continuous cycle. If yours stays running it may be hard on your compressor, I'm not sure about that though.