Rear Suspension Low

The rear of my '98 Eldorado is very low.. I don't hear the sound of the air pump ever.. supposed to come on 27 to 55 seconds after starting.
Question is .. where is the signal to turn this on after the initial delay? I know that the sensors determine whether to pump or exhaust depending upon load, but that is afterwards!
It's the initial delay that I'm trying to trace and cannot seem to find where it comes from!

I hope that I didn't offend Arnott by asking the question above.. If anyone reading this knows the answer, I'd really appreciate hearing from you! Any Cadillac mechanics on the Forum??