An air spring (air bag) replaces traditional steel coil or leaf springs. It consists of a tough, reinforced rubber cylinder sealed between metal mounting plates. An onboard compressor pumps air into the bladder to support the vehicle's weight. The air inside compresses to absorb road bumps, offering a smooth ride. By adjusting the air pressure, you can change the stiffness and ride height of the vehicle.
Rubber air bags degrade from age, ozone exposure, and road grit. They develop tiny dry-rot cracks around the lower folds. These cracks turn into leaks, forcing the compressor to run constantly to maintain ride height. This eventually burns out the compressor motor, leaving the suspension sitting flat on its frame.