The Bendix A9-D is an air dryer used as a filtration system for air brake compressors on 18-wheelers and other large vehicles. All large trucks with air brakes have air compressors, which keep the brake air tanks full so the truck can always stop when necessary. Since all air contains some humidity, the cooling of this humidity as it travels through compressors discharge lines can cause pools of water to gather at the bottom of the air tanks. The Bendix A9-D dries and removes contaminants trapped inside the "dessicant cartridge" --- the filter for the air dryer. You must replace the Bendix A9-D Dryer filter, or dessicant cartridge, when it becomes dirty.
Access the vehicle's motor, and locate the air compressor for the air brake system. The air compressor is mounted on the side of the engine block. However, the side of the engine block on which the compressor is located may vary depending on the make and model of your rig. Locate the Bendix A9-D, a black object resembling a standard oil filter but larger. It will be mounted either directly below or on the side of the compressor.
Loosen the nut holding the metal clamp in place at the top of the filter using a wrench. Work the clamp, with the nut still inside it but loosened, off the top of the dryer body head.
Work the cover of the air dryer off by hand, or with a pipe wrench if necessary, by twisting it slightly back and forth and then pulling up on it.
Remove the old filter from the dryer canister by hand, and install the new filter.
Replace the dryer's cap, then slip the tightening bracket over it. Tighten the bracket retaining nut with your wrench.
