Rear air suspension problem on a 95 deville. i hear the compressor go on yet once the car is drive a service suspension light comes on

In my opinion the air ride suspension is one of automobile's biggest mistakes. I see this a lot.

The first thing you must do is isolate the problem.

Jack up the back of the car and remove the rear wheels.

Now your shocks are visible. Inspect the rubber boots in the midsection of the shock, If this is worn or torn they will need to be replaced as they dry out once the integrity of the boot is jeopardized.

Next turn the key forward to turn in the compressor that you hear. And follow the thin black air lines that run into the side of the shock. A lot of times, especially on a vehicle this age, these lines will at some point rub on the frame or other item and have holes. Just listening for air leaks and running your fingers along the lines (feeling for bumps or holes) will give you a quick answer on this.

The only thing left in the system is the compressor itself, just remove the air lines from the shocks and as the compressor runs feel the end for air pressure. If you feel it the compressor is working.

Once you have isolated the issue your vehicle faces, feel free to come back and ask for assistance in replacing them. Be thourough and check everything though because 1 bad element will make future problems inevitable.

Please feel free to rate my answer and come on back to FixYa anytime.