air suspension compressor will not run?

Yep, most of the time the compressor motor goes bad due to moisture. Here are the fuses to check. Check out the images (below). Let us know how it goes

I have a 2000 expedition it has air ride suspension and the air compressor will not come on again I jumped it an it ran I replaced the sensor behind the bumper things still dose not work and do you know where the relay is for this system

It's located behind the right headlamp, ahead of the pump.

To test relay, (located below the passenger side headlight). At the 4 wire relay connector, check the Light Blue/Pink wire for battery voltage from fuse #109 50A in the Power Distribution Box under the hood. Check the Light Green/Red wire for a good ground. If OK, back probe the Dark Blue/Yellow wire and jump to ground. The relay should click and battery voltage should be present on the Gray/Red wire to the air suspension compressor. If there is no voltage on the GY/R wire with the DB/YE wire grounded, check connection at the relay. If OK, replace the relay and recheck operation. I have seen the relay connection corrode and in some cases the wire harness/wires rubbed thru near relay.