Cadillac Repair: Cadillac Suspension Problems, air ride suspension, cadillac sts

Question
I have 1999 Cadillac STS.  The air ride suspension is not inflating.  I don't hear a compressor coming on.     The car in dash display states service suspension.  Where is the air compressor located?

Any thoughts would be great.

Answer
The air compressor is located above the axle under the car.

The most common fault is the HEIGHT SENSOR which has a round black electrical plug that plugs into a black box about 4" square and has a metal arm that extends from the box to the axle also located under the car above the rear axle.