How can I manually add air to the factory shocks on a 98 deville?

Remove the plug from the coolent line, and gound them out as to close the switch, thus making the compressor think it has pressure to run, then you can add your coolent to proper lvl, the plug your wires back in.

Loosen the fittings on both lines of the compressor a little bit. One should pull air in and the other exhausts. Clutch needs to be engaged and the regulator open. Be careful, they pump hi pressure.

Check the pressure that the compressor is putting out.
It may need adjusting to give the shockies more pressure

You can't without a ton of adapters & fittings. Options: replace compressor or replace air shocks with aftermarket air shocks that you have to manually fill or replace with standard replacement shocks.

You can, but they won't adjust like your factory ones (automatically) Lots of folks replace w/aftermarket shocks instead of depending on factory units.

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.

You should have coil over stuts/shocks. On the rear you will have to put a coil kit on, but the front is ready to be changed. All you have to do is replace the air shocks with normal shocks with coil springs/helper springs. You can normally find these kits at auto supply stores, but you can also find them online, and possibly eBay. Make sure to shop around before you make a purchase. Your other option is to replace your air bags with lifter shocks. You would run the air lines to a convenient place where you can air them up manually. This would allow you to change the height of the car and the ride of the car. But this will make the "Cadillac ride" become more of a truck feel. Hope this helps you with your decision.

I have a 1998 Deville and both rear coil springs are broken.. It also has the air shocks that I dont think work.. Can I put regular shocks in and is there a after market coil spring out there for it ??

you may want to buy regular heavy duty shocks and put on the car to raise the back up high enough to do what you are trying to do.

You may have either leaking shocks. follow the air line from the shock to the compressor.